The circulatory system is not highly developed. No heart has been discovered. The whole body is pmencated by channels which have no proper coat In most genera of the Lepadidm the nervous system consists of six main ganglia, namely, the supresesophageal and five thoracic ganglia. Of these the first thoracic or infrnsusophngeal ganglion-is considerably the largest and most massive. It is squarish, or oval, or heart-shaped ; it presents no trace of being formed of two lateral ganglia. Two groat nerves spring from its under side, and run straight down amongst the viscera. These nerves are about as large as those forming the collar and those running to the second ganglion ; hence nix great nerves meet here, two in front, two behind, and two on the under side. Nerves are given off from the remaining ganglia to the cirri and other organs. The muscles of the capitulum are supplied from the nupra cesophageal ganglion.
Diagram of the anterior portion of the nervous system in Lepas faseieuinris. A, first thoracic or ganglion ; B, second thoracic ganglion ; C, third thoraclo ganglion ; D, aupra-msophageal ganglion ; E, the two ophthalmic ganglia ; F, double eye ; a, nerve going to first eirrbua; b, to tho muscles below the first cirrhus ; e, to the second elrrhus; d, to the third ; e, nerves running to the ovarin; J doublo nerves supplying the sac and peduncle, Nerves proceed from the supraetesophageal to the double eye of Lepers fasciev,larie. The idea that the whole peduncle and capitulunt consists of the first three segments of the head is beautifully sup ported by the structure of the nervous system, in which these parts are seen to be supplied with nerves exclusively from the supra (esophageal ganglion. In ordinary Crastatere the nupra-cesophageal ganglion sends nerves to the eyes and the two pairs of antenna) corresponding to the first three segments of the body.
The reproductive system of the Cirripedes has excited much interest from the results of the researches of Mr. Darwin. All the Cirripedes, with few exceptions, are bisexual, but Mr. Darwin has found that the masculine power of certain hermaphrodite species of 161e and Seal pellum is rendered more efficient by certain parasitic males, which, from their not pairing, as in all hitherto known cases, with females, but with hermaphrodites, Mr. Darwin designates Complemental Males. The ordinary male organs consist of pear- or finger-shaped bodies of a leaden colour, which coat the stomach, enter the pedicles, and even the basal segments of the rami of the cirri, and in some genera occupy certain swellings on the thorax and presents.
With regard to the ovaria, M. Martin-Saint-Ange has described how the peduncle is gorged with an inextricable mass of branching ovarian tubes filled with pannier matter and immature ova. The ova when excluded remain m the sae of the animal until the larva are hatched. They are very numerous, and generally form two concave nearly circular leaves, called by Darwin Ovigerous Lamellae The ova lie in a layer, from two to four deep, and all are held together by n moat delicate transparent membrane, which separately enfolds each ovum. This membrane is often thicker and stronger round the margins of the lamellte, where they are united in a peculiar manner, presently to be described, to a fold of akin on each aide of the sac ; these two folds Darwin calls the Ovigeroua Frmna. As the lamella are formed without organic union with the parent they would be liable to be washed out of the widely-opened sac of the Lepadider if they had not been specially attached to the frxna.
The complemental males, to which we have before alluded, occur in the genera Ibla, Scalpellum, A lcippe, and Cryptophialus; and these males are permanently attached to the females. In Ibla the male is attached within the sac of the female; it has a well-organised mouth supported on a peduncle, but with only a rudiment of the thorax, and with only two pairs of aborted cirri. In Scalpellunt the males differ in the different species remarkably in structure ; in some of the species they are not very unlike ordinary Pedunculated Cirripedes, and are attached between the acute of the females ; in other species the males are very rudimental, extremely minute, and would never without close examination have been thought to have even belonged to the class Cirripedia. These males consist of a sac, with rudiments of four valves, inclosing a singularly modified thorax, with only four pairs of appendages (which cannot be called cirri); they are entirely destitute of a mouth or stomach. The males of Cryptophialus and Alcippe are even more rudimentary than those of the above species of Scalpellunt : they are reduced to an outer envelope (homologous with the carapace of ordinary Crustacea), to a single eye, the testis, vesicula aeminalis, and a wonderfully elongated probosciformed male organ'. Hence
there is no mouth, no stomach, no thorax, no abdomen, and no appendages or cirri. It may be doubted whether in the whole animal kingdom there exists a (creature in a more rudimentary condition than these males. As they do not possess a mouth or stomach they are necessarily short-lived. The pupa fixes itself on the female, becomes cemented to her, undergoes its metamorphosis, and becomes a male Cirripede; the spermatozoa become developed and are discharged ; the male dies, decays, and genemllg drops off, and is succeeded, when the ova in the female are next ready to be impregnated, by one or more fresh males. Owing apparently to the small size of the males, there is generally more than one attached to the female at the same time ; and in the case of Alcippe lampas Mr. Darwin found no less than thirteen of these singular parasitic and rudimentary males attached to a single female Remarkable as is the occurrence of the above male parasites on the females, it is a far more singular fact, that in some of the species of Ibla and Scalpellunt, the males are attached, not on females, hut on hermaphrodites ; and hence they have been called by Mr. Darwin Complemental-Males, inasmuch as they are complementary to the male organs of the hermaphrodite. Mr. Darwin, in his work on the Cirripedia (p. 231), published by the Ray Society, enters at length on the evidence in support of this view, and be believes the facts cannot be coutroverted. (p. 214.) " Although the existence of hermaphrodites and males within the limits of the same species is a new fact amongst animals, it is far from rare in the vegetable king dom: in stich cases the male flowers are sometimes In a rudimentary condition compared to the hermaphrodite flowers, exactly in the same manner as are the males of IbItt and Scalpellum. If the final cause of the existence of these Complemental Males be asked, no certain answer can be given; the vesicula seminales in the hermaphrodite of Ibla quadriralris, and in some species of Scalpelluns, appeared to be of small diameter; but on the other hand the ova to be impregnated are fewer than in most Cirripedes. No explanation can be given of the much simpler case of the mere separation of the sexes in the four genera before enumerated ; nor can any explanation be given of the much more varied arrangement of the parts of fructification in plants of the Linnean class Polygantia." The following woodcuts will give an idea of he structures above described, more especially in accordance with the views of Martin Saint-A nge : Fig. 1. A natife jaune sans coquille (Cuvier, Afepas1 ) : A, a gelatinous production, the cement, which serves to fix the peduncle ; B, the first membrane of the peduncle; B' a small Cirripede, of the natural size developed upon the peduncle of the parent ; C, the capitulum, which contains the body of the animal ; D. the fissure of the capitu lum from which issue the feet or cirri F. The point F indicates the termination of the peduncle, and the place where the eggs atop; (1, the eggs arrived within the sac. Fig. 2. The same letters refer to the same partsas in fig. 1; H, the pedicles of the cirri, which sustain the rami, F. At the base of the feet (H) are four branchire; and between these feet and those placed on the other side is seen the recurved tube which serves to convey the seminal liquor to the ova within the sac. Fig. 3. The same Cirripede, from which thg half of the first envelope has been taken so as to expose the interior. The peduncle contains a second cylinder terminated in a cul-de-sac by its inferior extremity, and covered at the other by ,a very deli cate membrane; the longitudinal and transverse muscular fibres may be observed ; e, e, indicate the canal which, according to Saint-Ange, carries the eggs of the peduncle within the SAC b, that which serves as a nourishing vessel to the peduncle and the eggs ; g, g, the mem brane of the sac which intercepts all direct communication between the peduncle and the cavity of the sac. J represents the body of the Cirripede inclosed in its proper envelope. Fig. 4. The same situa tion as the last, representing all the membranes which envelop the body of the Cirripede ; B, B, the muscular cylindrical pipe open, in which the eggs are seen ; e, r, the course of the ovarian tubes in the thickness of the second envelope; g,g,g, the envelope opened and turned back ; J, J, J, the proper membrane of the body of the animal ; it is with this cavity that the canal b communicates, and it is between this proper membrane and that of the second envelope g, g, g, that the eggs are found : whence it results that the cavity of the mantle has no com munication with the peduncle, except by means of the oviduct e.