A Monograph on the Sub-class Cirripedia Part 27

| | | | | | |Ultimate segment, length of. Scale | | | | | | |same.

| | | | | | | |Ultimate segment, width of.

| | | | | | | |Scale, fractions of the | | | | | | | |1/20,000ths of an inch.

LEPAS: disc large, thin, almost _circular_, slightly elongated, with several long spines on the hinder margin; end segment with three very long, plumose spines on the upper _exterior_ angle.[61]

|_L. anatifera_ (?) | |62 | | |-- | | | |20 | | | | |23 | | | | | |22 | | | | | | |-- | | | | | | | |--

|_L. australis_, | |111 | | |-- | | | |40 | | | | |42 | | | | | |39 | | | | | | |18 | | | | | | | |30

|_L. pectinata_, | |51 | | |-- | | | |23 | | | | |16 | | | | | |14 | | | | | | |9 | | | | | | | |16

|_L. fascicularis_, | |60 | | |40 | | | |22 | | | | |16 | | | | | |15 | | | | | | |-- | | | | | | | |--

DICHELASPIS: disc _small_, thin, circular, with several spines on the hinder margin; end segment, with two long spines on the upper _exterior_ angle.

|_D. Warwickii_, | |54 | | |-- | | | |11 | | | | |7-8 | | | | | |7-8 | | | | | | |6 | | | | | | | |13-14

CONCHODERMA: disc large, thin, _transversely_ elongated, with several long spines on the hinder margin; end segment, with two excessively long, plumose spines on the upper _exterior_ corner.

|_C. virgata_, | |82 | | |40 | | | |28 | | | | |25 | | | | | |35 | | | | | | |12 | | | | | | | |26

|_C. aurita._ | |-- | | |-- | | | |-- | | | | |28 | | | | | |40 | | | | | | |11 | | | | | | | |26

ALEPAS: disc small, slightly elongated, with two or more spines on the hinder margin; end segment, with two long spines on the upper _inner_ corner, and four shorter ones on the exterior corner.

|_A. cornuta_, | |60 | | |-- | | | |24 | | | | |14 | | | | | |12 | | | | | | |8 | | | | | | | |20

IBLA (parasitic males of): disc, _hoof-like_, _pointed_, elongated, with a single spine on the hinder margin; end segment, with four short spines on the upper exterior corner.

|_I. c.u.mingii_, | |22 | | |-- | | | |7-8 | | | | |7 | | | | | |-- | | | | | | |3-4 | | | | | | | |7-8

|_I. quadrivalvis_, | |32-33 | | |-- | | | |10 | | | | |8 | | | | | |5 | | | | | | |4 | | | | | | | |8

SCALPELLUM: disc _hoof-like_, generally _pointed_ and elongated, with a single spine on the hinder margin; end segment, with a notch on the inner[61] side, bearing two spines, longer than on the exterior corner.

|_S. vulgare_, | |39 | | |19 | | | |10 | | | | |10-11 | | | | | |5-6 | | | | | | |6 | | | | | | | |7

|_S. ornatum_, | |36 | | |21 | | | |10 | | | | |12 | | | | | |-- | | | | | | |-- | | | | | | | |--

|_S. Peronii_, | |30 | | |19 | | | |-- | | | | |9 | | | | | |6 | | | | | | |5 | | | | | | | |10

POLLICIPES: disc small, _hoof-like_, not pointed, with a single spine on the hinder margin; end segment, as in _Scalpellum_.

|_P. cornucopia_, | |20 | | |-- | | | |6 | | | | |6 | | | | | |6 | | | | | | |6 | | | | | | | |8

[61] In the diameter of the disc, the thin membranous border, which is present in the first three genera, is included; but I have some doubts, whether this border be not the first rim of cementing tissue, as all the specimens, of which measurements are here given, had been removed after attachment. In using the terms inner and outer sides of the end segment, it is supposed, that this segment is stretched straight forwards, instead of being bent rectangularly outwards, as in its natural position; and then there can be no doubt which is the inner and outer sides.

It should be observed that the evidence in this summary is of a c.u.mulative nature. If we think it highly, or in some degree probable,--from the ordinary form of _Ibla c.u.mingii_ having been shown on good evidence to be exclusively female,--from the absence of ova and ovaria in the a.s.sumed males of both species of Ibla, at the period when their vesiculae seminales were gorged with spermatozoa,--from the close general resemblance between the parts of the mouth in the parasites and in the Iblas to which they are attached,--from the differences between the two parasites being strictly a.n.a.logous to the differences between the two species of Ibla,--from the generic character of their prehensile antennae,--and from other such points,--if from these several considerations, we admit that these parasites really are the males of the two species to which they adhere, then in some degree the occurrence of parasitic males in the allied genus Scalpellum is rendered more probable. So the absolute similarity in the antennae of the males and hermaphrodites both in _S. vulgare_ and _S. Peronii_; and such relations as that of the relative villosity of the several species in this same genus, all in return strengthen the case in Ibla. Again, the six-valved parasites of _S. Peronii_ and _S. villosum_ are so closely similar, that their nature, whatever it may be, must be the same; hence we may add up the evidence derived from the ident.i.ty of the antennae in the parasite and hermaphrodite _S. Peronii_, with that from the antennae in the male _S. villosum_, approaching in character to Pollicipes, to which genus the hermaphrodite is so closely allied; and to this evidence, again, may be added the singular coincident absence of caudal appendages in the male and hermaphrodite _S. villosum_. If these two six-valved parasites be received as the complemental males of their respective species, no one, probably, will doubt regarding the nature of the parasite of _S.

rostratum_, in which the direct evidence is the weakest; but even in this case, the particular point of attachment, and the state of development of the valves, form a link connecting in some degree, the parasites of the first three species with the last two species of Scalpellum, in accordance with the affinities of the hermaphrodites.

When first examining the parasites of _S. rostratum_, _S. Peronii_, and _S. villosum_, before the weight of the c.u.mulative evidence had struck me, and noting their apparent state of immaturity, it occurred to me that possibly they were the young of their respective species, in their normal state of development, attached to old individuals, as may often be seen in Lepas; this, however, would be a surprising fact, considering that _S. rostratum_ and _S. Peronii_ are ordinarily attached, in a certain definite position, to h.o.r.n.y corallines, and considering that the exact points of attachment in these three parasites, (of which I have seen no other instance amongst common Cirripedes,) namely, between the scuta, would inevitably cause their early destruction, either directly or indirectly, by their living supports being destroyed. Nevertheless, I carefully examined a young specimen of _S. rostratum_ only thrice as large as the parasite; and not having very young specimens of _S.

Peronii_ and _villosum_, I procured the young of closely-allied forms, namely, of _S. vulgare_, (with a capitulum only 4/100th of an inch in length,) and of _Pollicipes polymerus_, (with a capitulum of less size than that of one of the parasites,) and there was not the least sign of anything abnormal in the development of the valves. In _S. vulgare_, at a period when the calcified scuta could have been only 1/100th of an inch in length, (and therefore considerably less than the scuta in the parasites,) the upper latera must have been as much as 4/1000ths of an inch in length, and the valves of the lower whorl certainly distinguishable.

To sum up the evidence on the s.e.x of the parasites, I was not able to discover a vestige of ova or ovaria in the two male Iblas; and I can venture to affirm positively, that the parasites of _S. Peronii_ and _S.

villosum_ are not female. On the other hand, in the two male Iblas, I was enabled to demonstrate all the male organs, and I most distinctly saw spermatozoa. In the parasitic complemental male of _S. vulgare_, I also most plainly saw spermatozoa. In the parasites of _S. rostratum_, _S. Peronii_, and _S. villosum_, the external male organs were present.

I may here just allude to the facts given in detail under Ibla, showing that it was hardly possible that I could be mistaken regarding the exclusively female s.e.x of the ordinary form of _I. c.u.mingii_, seeing how immediately I perceived all the male organs in the hermaphrodite _I.

quadrivalvis_; and as the parasite contained spermatozoa and no ova, the only possible way to escape from the conclusion that it was the male and _I. c.u.mingii_ the female of the same species, was to invent two hypothetical creatures, of opposite s.e.xes to the Ibla and its parasite, and which, though Cirripedes, would have to be locomotive! I insisted upon this alternative, because if the parasite of _I. c.u.mingii_ be the male of that species, then unquestionably we have in _I. quadrivalvis_ a male, complemental to an hermaphrodite,--a conclusion, as we have seen, hardly to be avoided in the genus Scalpellum, even if we trust exclusively to the facts therein exhibited.

With respect to the positions of the parasitic males, in relation to the impregnation of the ova in the females and hermaphrodites, it may be observed that in the two male Iblas, the elongated moveable body seems perfectly adapted for this end; in the males of the first three species of Scalpellum, the spermatozoa, owing to the manner in which the thorax is bent when protruded, would be easily discharged into the sack of the female or hermaphrodite; this would likewise probably happen with the complemental male of _S. rostratum_, considering its position within the orifice of the capitulum, between the mouth and the adductor scutorum muscle. The males of _S. Peronii_ and _villosum_ being fixed a little way beneath the orifice of the sack, below the adductor muscle, are less favorably situated, but the spermatozoa would probably be drawn into the sack by the ordinary action of the cirri of the hermaphrodite, and therefore would at least have as good a chance of fertilising some of the ova, as the pollen of many dioecious plants, trusted to the wind, has of reaching the stigmas of the female plants. Regarding the final cause, both of the simpler case of the separation of the s.e.xes, notwithstanding that the two individuals, after the metamorphosis of the male, become indissolubly united together, and of the much more singular fact of the existence of Complemental males, I can throw no light; I will only repeat the observation made more than once, that in some of the hermaphrodites, the vesiculae seminales were small, and that in others the probosciformed p.e.n.i.s was unusually short and thin.

Viewing the parasitic males, in relation to the structure and appearance of the species to which they belong, they present a singular series. In _S. Peronii_ and _S. villosum_, the internal organs have the appearance of immaturity; the shape of the capitulum is specially modified for its reception between the scuta of the hermaphrodite, and several of the valves have not been developed. This atrophy of the valves, is carried much further in _S. rostratum_. In Ibla, many of the parts are embryonic in character, but others mature and perfect; some parts, as the capitulum, thorax, and cirri, are in a quite extraordinary state of atrophy; in fact, the parasitic males of Ibla consist almost exclusively of a mouth, mounted on the summit of the three anterior segments of the 21 normal segments of the archetype crustacean. In the males of the first three species of Scalpellum, some of the characters are embryonic,--as the absence of a mouth, the presence of the abdominal lobe, and the position of the few existing internal organs; other characters, such as the general external form, the four bead-like valves, the narrow orifice, the peculiar thorax and limbs, are special developments. These three latter parasites, certainly, are wonderfully unlike the hermaphrodites or females to which they belong; if cla.s.sed as independent animals, they would a.s.suredly be placed not in another family, but in another Order. When mature they may be said essentially to be mere bags of spermatozoa.

In looking for a.n.a.logies to the facts here described, I have already referred to the minute male Lerneidae which cling to their females,--to the worm-like males of certain Cephalopoda, parasitic on the females,--and to certain Entozoons, in which the s.e.xes cohere, or even are organically blended by one extremity of their bodies. The females in certain insects depart in structure, nearly or quite as widely from the Order to which they belong, as do these male parasitic Cirripedes; some of these females, like the males of the first three species of Scalpellum, do not feed, and some, I believe, have their mouths in a rudimentary condition; but in this latter respect, we have, amongst the Rotifera, a closely a.n.a.logous case in the male of the Asplanchna of Gosse, which was discovered by Mr. Brightwell[62] to be entirely dest.i.tute of mouth and stomach, exactly as I find to be the case with the parasitic male of _S. vulgare_, and doubtless with its two close allies. For any a.n.a.logy to the existence of males, complemental to hermaphrodites, we must look to the vegetable kingdom.

Finally, the simple fact of the diversity in the s.e.xual relations, displayed within the limits of the general Ibla and Scalpellum, appears to me eminently curious; we have (1st) a female, with a male (or rarely two) permanently attached to her, protected by her, and nourished by any minute animals which may enter her sack; (2d) a female, with successive pairs of short-lived males, dest.i.tute of mouth and stomach, inhabiting two pouches formed on the under sides of her valves; (3d) an hermaphrodite, with from one or two, up to five or six similar short-lived males without mouth or stomach, attached to one particular spot on each side of the orifice of the capitulum; and (4th) hermaphrodites, with occasionally one, two, or three males, capable of seizing and devouring their prey in the ordinary Cirripedial method, attached to two different parts of the capitulum, in both cases being protected by the closing of the scuta. As I am summing up the singularity of the phenomena here presented, I will allude to the marvellous a.s.semblage of beings seen by me within the sack of an _Ibla quadrivalvis_,--namely, an old and young male, both minute, worm-like, dest.i.tute of a capitulum, with a great mouth, and rudimentary thorax and limbs, attached to each other and to the hermaphrodite, which latter is utterly different in appearance and structure; secondly, the four or five, free, boat-shaped larvae, with their curious prehensile antennae, two great compound eyes, no mouth, and six natatory legs; and lastly, several hundreds of the larvae in their first stage of development, globular, with horn-shaped projections on their carapaces, minute single eyes, filiformed antennae, probosciformed mouths, and only three pair of natatory legs; what diverse beings, with scarcely anything in common, and yet all belonging to the same species!

[62] 'Annals of Natural History,' vol. ii, (2d series, 1848,) p.

153, Pl. vi. Mr. Dalrymple has published a very interesting paper on the same subject in the 'Philosophical Transactions,' (p.

342,) 1849; and there is another Memoir by Mr. Gosse in the 'Annals of Natural History,' vol. vi, (1850,) p. 18.

_Genus_--POLLICIPES. Pl. VII.

POLLICIES. _Leach._ Journal de Physique, tom. lx.x.xv, Julius, 1817.[63]

LEPAS. _Linn._ Systema Naturae, 1767.

ANATIFA. _Brugiere._ Encyclop. Method. (des Vers), 1789.

MITELLA. _Oken._ Lehrbuch der Naturgeschichte, 1815.

RAMPHIDIONA. _Schumacher._ Essai d'un Nouveau Syst. &c., 1817 (ante Julium).

POLYLEPAS. _De Blainville._ Dict. des Sc. Nat., 1824.

CAPITULUM (secundum Klein). _J. E. Gray._ Annals of Philos., tom.

x, new series, Aug. 1825.

[63] This is one of the rare cases in which, after much deliberation, and with the advice of several distinguished naturalists, I have departed from the Rules of the British a.s.sociation; for it will be seen that _Mitella_ of Oken, and _Ramphidiona_ of Schumacher, are both prior to _Pollicipes_ of Leach; yet, as the latter name has been universally adopted throughout Europe and North America, and has been extensively used in geological works, it appears to me to be as useless as hopeless to attempt any change. It may be observed that the genus _Pollicipes_ was originally proposed by Sir John Hill ('History of Animals,' vol. iii, p. 170), in 1752, but as this was before the discovery of the binomial system, by the Rules it is absolutely excluded as of any authority. In my opinion, under all these circ.u.mstances, it would be mere pedantry to go back to Oken's 'Lehrbuch der Naturgeschichte' for the name _Mitella_,--a work little known, and displaying entire ignorance regarding the Cirripedia.

_Valvae ab 18 usque ad 100 et amplius: lateribus verticilli inferioris multis; lineis incrementi deorsum ordinatis: sub-rostrum semper adest: pedunculus squamiferus._

Valves from 18 to above 100 in number: latera of the lower whorl numerous, with their lines of growth directed downwards: sub-rostrum always present: peduncle squamiferous.

Hermaphrodite; filamentary appendages either none, or numerous and seated on the prosoma and at the bases of the first pair of cirri; labrum bullate; trophi various; olfactory orifices generally highly prominent; caudal appendages uni-articulate and spinose, or multi-articulate.

Attached to fixed, or less commonly to floating objects, in the warmer temperate, and tropical seas.

It has been remarked, under Scalpellum, how imperfectly that genus is separated from Pollicipes; and we have seen under _Scalpellum villosum_ that the addition of a few small valves to the lower whorl, would convert it into a Pollicipes, most closely allied to _P. sertus_ and _spinosus_. It has also been shown, that the six recent species of Pollicipes might be divided into three genera, of which _P. cornucopia_, _P. elegans_, and _P. polymerus_, would form one thoroughly natural genus, as natural as Lepas and the earlier genera; _P. mitella_ would form a second; and _P. sertus_ and _P. spinosus_ a third; but I have acted to the best of my judgment in at present retaining the six species together. As far as the valves of the capitulum are concerned, it would be very difficult to separate _P. mitella_ from _P. sertus_ and _spinosus_.