Charles Darwin

“ Scalpellum, a class of allied facts to be advanced, which in some respects support the view here taken, but in others are so remarkable and so hard to be believed, that I will call attention to the alternative, if the above view be rejected. The ordinary Ibla Cumingii must have a male, for that it is not an hermaphrodite can hardly be questioned, seeing how easy it always is to detect the male organs of generation; and we must consequently believe in the visits of a locomotive male, though the existence of a locomotive Cirripede is improbable in the highest degree. ”

“ So again in S. rutilum, the shape of the scutum seems adapted for the reception of the male, in a manner which must be attributed to its own growth, and not to the pressure or attachment of a foreign body. Now there is a strong and manifest improbability in an animal being specially modified to favour the parasitism of another, though there are innumerable instances in which parasites take advantage of pre-existing structures in the animals to which they are attached. ”

“ I have used the term parasitic, which perhaps ought strictly to be confined to cases where one creature derives its nutriment from another, inasmuch as the male is invariably and permanently attached to and imbedded in the female,—from its being protected by her capitulum, so that its own capitulum is not developed—and from its feeding on minute animals infesting her sack. ”

“ The valves are placed either at some distance from each other, or close together; but their growing margins very rarely overlap each other, though this is sometimes the case with their upper, free, tile-like apices; in a few species the scuta and terga are articulated together, or united by a fold. The membrane connecting the valves, where they do not touch each other, is like that forming the peduncle, and is sometimes brilliantly coloured crimson-red; generally, it appears blueish-gray, from the corium being seen through. ”

“ As the individuals grow and increase in size, so do the glands and cement-ducts; but it seems often to happen, that when a specimen is immovably attached, the cementing apparatus ceases to act, and the cellular contents of the duct become converted into a thread of transparent tough cement; the investing membrane, also, of the ducts, in Conchoderma sometimes becomes hard and mamillated. I have already alluded to the case of a Pollicipes, in which both glands and ducts, and even a small portion of the two adjoining ovarian tubes, had become thus filled up. ”

“ In the larva the cement always escapes through the prehensile antennæ; and it thus continues to do throughout life in most or all of the species of Lepas, Conchoderma, Dichelaspis and Ibla. In the first two of these genera, the cement escapes from the borders of the lower side of the disc or penultimate segment of the antennæ, and can be there seen radiating out like spokes, which at their ends divide into finer and finer branches, till a uniform sheet of cement is formed, fastening the antennæ and the adjoining part of the peduncle down to the surface of attachment. ”

“ I do not understand how the splitting of the old membrane is effected; but no doubt it is by the same process by which the membrane of the capitulum in other genera, as in Scalpellum, splits symmetrically between the several valves. In the branched filaments it is particularly difficult to understand their growth, for it is not possible, after examining them, to doubt that they continue to increase, and send off sub-branches, which it would appear probable, penetrate the shark’s flesh like roots. ”

“ Ange: like others, I have failed, as yet, in discovering a heart. The whole body is permeated by channels, which have not any proper coat: there is one main channel along the ventral surface of the thorax, dividing and surrounding the mouth, and giving out branches which enter the inner of the two channels in each cirrus: as Burmeister has shown, there are also two channels in the penis. There are two dorso-lateral channels in the prosoma, which are in direct connection with the great main channel, running down the rostral (i. e., ventral) side of the peduncle. ”

“ I may, however, remark that in Scalpellum, the scuta first grow downwards, and afterwards in most of the species upwards, whereas here from the beginning, the growth is both upwards and downwards. In the mouth and cirri, there is rather more resemblance to Scalpellum than to Pæcilasma and Lepas: in habits, also, this genus agrees with Scalpellum, and if it had possessed a lower whorl of valves, it would have quite naturally entered that genus. It is unfortunate, that so insignificant and poorly characterised a form should require a generic appellation. ”

“ As the whole of the peduncle is imbedded, and as the mouth is probosciformed, with the labrum a little curled over the adductor muscle, I conclude that this Cirripede can reach minute animals crawling by on the surface of the shark’s body.
It must be borne in mind that the mouth, as in all Cirripedes, has the power of independent movement, and that the mandibles and maxillæ are here beautifully adapted to catch and force down any small living creature into the muscular œsophagus ”

“ The larvæ, I conclude, crawl in at the orifice, one side of which is formed, as we have seen, of yielding membrane, and scratch out the dead exuviæ of the former occupant: certainly, the males are less firmly attached to their pouches, though some small quantity of cement is excreted, than are other Cirripedes to the objects to which they are attached. The small size of the female, and her valves not being thickly edged with chitine, accounts for the males having pouches specially formed for them, instead of being, as in S. vulgare, laterally imbedded in the chitine-border of the scuta. ”

“ The inner surface of each scale is triangular, with the basal margin protuberant. The scales continue to grow or be added to, only in about the ten upper whorls, which form but a small part of the whole peduncle; in the lower part, the scales become further and further separated from each other. The surface of attachment, in full-grown specimens, is broad; but in two very young specimens, which I removed with great care after the action of potash, I found the peduncle ending in a filiform prolongation, such as often occurs in Scalpellum vulgare and in Lepas fascicularis. ”

“ I was able to distinguish that the two lower pair of spines on the ventral surface, are seated a little way one below and within the other, as in S. vulgare. The abdominal spines altogether form quite a brush, and there are certainly several more than in S. vulgare, and those on the two sides are much longer.
Antennæ.—The disc is hoof-like, with the upper surface forming a straight line with the upper edge of the basal segment; the apex is pointed and clothed with some fine down; there is a single spine pointing backwards, which rises from the lower flat surface. ”

“ The male Ibla must seize its prey, guided probably by its well-developed olfactory organs, through the movement of its long, flexible body, furnished with muscles, and with the mouth seated on the summit. We have already seen one instance of a Cirripede, the Anelasma, obtaining its food without the aid of cirri, by means of its probosciformed, flexible mouth. The eye can serve only to announce to the male when the female opens her valves, allowing occasionally some minute prey to enter. ”

“ The delicate tunic lining the sack, (a mere duplicature of that thick one, forming the outside of the capitulum, and generally transformed into valves,) and the integuments of the whole body, are regularly moulted. With these integuments, the membrane lining the œsophagus, the rectum, and the deep olfactory pouches, and the horny apodemes of the maxillæ, are all cast together. I have seen a specimen of Lepas, in which, from some morbid adhesion, the old membrane lining one of the olfactory pouches had not been moulted, but remained projecting from the orifice as a brown shrivelled scroll. ”

“ Indeed it is not easy to imagine a better marked series of transitional forms, than those presented by the terga, in passing from L. dorsalis through L. Nicobarica, L. Rhodiopus, and L. truncata, to L. Valentiana. Lithotrya has most affinity to Scalpellum villosum or to Pollicipes spinosus and P. sertus; though the affinity is far from close. In these two species of Pollicipes, we have seen that large irregular calcified spines are formed at the base of the peduncle, whereas in the other Pedunculata the scales or spines are formed exclusively round the upper margin of the peduncle. ”

“ It deserves notice, that in the class Crustacea, both in the Lerneidæ and in the Cirripedia, the males more closely resemble the larvæ, than do the females; whereas amongst insects, as in the case of the glow-worm in Coleoptera, and of certain nocturnal Lepidoptera, it is the female which retains an embryonic character, being worm-like or caterpillar-like, without wings. But in all these cases, the male is more locomotive than the female. ”

“ The scuta and terga are always considerably larger than the other valves: in the different genera the valves differ so much in shape that little can be predicated of them in common; even the direction of their lines of growth differs,—thus, in Lepas and some allied genera, the chief growth of the scuta and of the carina is upwards, whereas in Pollicipes and Lithotrya, it is entirely downwards; in Oxynaspis, and some species of Scalpellum, it is both upwards and downwards. ”

“ The stomach is lined by unusually prominent biliary folds, which in the duodenum are transverse, sending forth, however, short folds at right angles; and these latter, in the proper stomach, become so much developed that the folds appear longitudinal. The rectum extends inwards, about as far as the base of the fourth pair of cirri, but is very short, owing to the little development of the three posterior segments of the thorax. The anus is seated in its usual place, at the dorsal basis of the penis, and is hidden by loose folds of skin; but there are no distinct caudal appendages. ”

“ The larva of the male must have a different instinct from the larva of the hermaphrodite; for the latter attaches itself head downwards to a coralline, whilst the male larva crawling on the scuta of the hermaphrodite, discovers, I presume by eye-sight, the fold in the shell beneath the translucent border of chitine, and there invariably attaches itself. ”

“ Professor Leidy does not mention the ophthalmic ganglia; hence I infer that in Balanus, which is a more highly organised Cirripede, they are fused into the supra-œsophageal ganglion.
In all the genera, the double eye is seated deep within the body; it is attached by fibrous tissue to the radiating muscles of the lowest part of the œsophagus, and lies actually on the upper part of the stomach; consequently, a ray of light, to reach the eye, has to pass through the exterior membrane and underlying corium connecting the two scuta, and to penetrate deeply into the body. ”

“ The testes are large, but the vesiculæ seminales in some of the species extraordinarily small. Scalpellum ornatum, and perhaps S. rutilum, are unisexual; the other species are hermaphrodite, but most or at least some of the individuals, are furnished with Complemental Males. These latter are fully described under each species, so I will here only remark, that S. ornatum, which alone (excepting perhaps S. rutilum) is unisexual, has less claim than the other species to be generically separated: we have seen also, in Ibla, that similar sexual differences occur in two most closely allied species. ”

“ I have already given my reasons for instituting and separating this genus from Lepas; as far as the capitulum is concerned, the differences between these genera certainly appear trivial; they consist in the carina not extending up between the terga, and in the lower end being either truncated, or produced into an imbedded disc: the terga have a single occludent margin. The included animal’s body differs in more important respects; for both mandibles and maxillæ are very distinct; the cirri of some of the species also differ ”

“ Affinities.—Ibla, though externally very different in appearance from Scalpellum, is more nearly related to that genus than to any other; in both genera some species have the sexes separate, the imperfect males being parasitic on the female, and other species are bisexual or hermaphrodite, but aided by parasitic complemental males. In Scalpellum, again, the œsophagus pursues a sinuous course, resembling that in Ibla, though it does not pass exteriorly to the adductor scutorum muscle. ”

“ Scuta, terga, carina, and rostrum, much larger than the other valves. All are moderately thick, placed rather distant from each other, covered with thick membrane which abounds with tubuli, arranged in rows; surface apparently smooth, but with a very high power, extremely minute spines can be seen at the extremities of almost all the tubuli. Little bunches of reddish fibrous matter are imbedded in the membrane, like tufts of sea-weed floating in water. ”

“ Small pointed [Pg 30] spines, connected with the underlying corium by tubuli, are not unfrequently articulated on this membrane: the tubuli, however, are often present where there are no spines. To allow of the growth of the capitulum, the membrane between the valves splits at each period of exuviation, when a new strip of membrane is formed beneath, connected on each side with a fresh layer of shell,—the old and outer slips of membrane disintegrating and disappearing: when there are many valves, the line of splitting is singularly complicated. ”

“ I trust, before long, that some naturalist, with more skill than I possess, will examine these parasites on Scalpellum vulgare, which unfortunately is the only species of the genus that can be easily obtained. Fresh specimens, or those preserved in spirits of wine, are necessary. The action of boiling caustic potash is very useful in cleaning the prehensile antennæ. If these latter organs are sought in the hermaphrodite for the sake of comparison, young specimens, adhering to clean branches of a coralline, should be procured, and caustic potash used. ”