Fig. 5. Side view of the common Duck Barnacle (Lepas analifera) taken out of the shell, enveloped in its proper membrane, under which is found the salivary (I) vesicle ; , the cervical ganglion ; r, the nerve which is given off from the brain to go to the muscles of the skin ; J, the two levator muscles of the upper lip ; K K, bmnehire ; h, a horny tubercle which is formed on each aide of the orifice of the vent ; U', the extremity of the tube, bearded with fine hairs. Fig. 6. Anterior view of the same, showing the truly articulated disposition of the body, each ring of which corresponds to a pair of feet • S, the adductor muscle of the valves ; U'. the articulated tube which contains the spermatic canal. Fig. 7. The intestinal canal of the same species; D, the mouth seen from the side ; d, the (esophagus; d', the stomach; d', the peduncle which makes this organ communicate with a species of csecum, d"', of the same structure and form as the stomach ' • T, the intestinal canal, offering two natural curvatures ; orifice of the rectum ; U U, vesiculie seminales, uniting in a single canal very delicate, and terminated at U' by a small orifice. Fig. 8. Disposition of the nervous system : 1. The first (esophageal ganglion, called the brain : from these united ganglions spring the branches r, r', r*, destined for all the muscles of the dorsal part, and two extremely delicate threads which go on each side, the first to the salivary vesicle V, the second to a new ganglion Z; 2. The second ganglion, sending two nervous branches to each jaw-foot F, and small branches to the (esophagus; 3, 4, 5, 6 correspond to the other ganglions ; 6 furnishes the two last pairs of feet. It is from the branches which go to the last feet, and not from the ganglions them selves, that the two threads y and g', which go to the extremity, U', of the tube are detached. The point x corresponds to the centre of the ossophagrui which has been removed.
The process of exuvintion takes place in the arrepalia. Yr. Darwin says, "In the Lepadichr, with the exception of the genus hithotrya, in which the calcareous scales on the peduncle together with the membrane connecting them is cast off, neither the valves nor the membrane uniting them, nor that forming the peduncle with its scales, are moulted ; but the surface gradually disintegrates, and is removed, perhaps sometimes in flakes; whilst new, and larger layers are formed beneath. In most Sessile Cirripedes the outside m embmne connecting the opereulum and shell is regularly moulted. The delicate tunic lining the sac and the integuments of the whole body are periodically shed. With these integuments, the membrane lining the (esophagus, the rectum, the deep olfactory pouches, and the horny apodemea of the maxilla are all moulted together. The new spines on the cirri are formed within the old ones.
"All Cirripedia grow rapidly ; the yawl of 11.31.S. Beagle was lowered into the water at the Galapagos Archipelago on the 15th of September, and after an interval of exactly thirty-three days was hauled in a;ain. I found on her bottom a specimen of Conchoderma rirgata with the capitnIum and peduncle., each half an inch in length and the former the in width; this is half the size of the largest specimen I have seen of this species. Several other individuals, not half the size of the above, contained numerous ova in their lamella, ready to burst forth. Supposing that the larvae of the largest specimen
became attached the first day the boat was put into the water, we have the metamorphosis, an increase of length from about of a inch, the size of the larva, to a whole inch, and the laying of probably several sets of eggs, all effected in thirty-three days. From this rapid growth repeated exuriations must be requisite. Mr. W. Thompson, of Belfast, kept twenty specimens of Balanus balanoides, a form of much slower growth, alive, and on the twelfth day he found the twenty-first integu ment, showing that all had moulted once, and one individual twice within this period. I may here add that the Pednneulated Cirripedes never attain so large a bulk as the Sessile. Lepas anatifera is Aome times 16 inches in length, but of this the far greater portion consists of the peduncle. Pollicino mild& is the most massive kind ; I have seen a specimen with a capita lurn two-thirds of an inch in width." The Pedunculated Cirripedes extend over the whole world ; and most of the individual species have large ranges, more especially, as might have been expected, those attached to floating objects. Excepting these latter, the greater number inhabit the warmer, temperate, and tropical seas. Of those attached to fixed objects, or to littoral animals, it is rare to find more than three or four species in the same locality. On the shores of Europe Mr. Darwin says he knows of only three, namely, Sealyham, Pollicipes, and A lepas. At Madeira (owing to the Admirable researchers of the Bev. It. T. Lowe) two Pseeitztentas, a DicAehurpis, and an Orynaspis are known. In New Zealand there are two Pollicino and an Alspae, and perhaps a fourth form. From the Philippine Archipelago, in the great collection made by Mr. Cuming, there are a Pad/arms, an a Sealpellem, Pollicino, and Lithotrya. Of all the Lepodidm nearly half are attached to floating objects or to animals which are able to change their position ; the other half arc generally attached to fixed organic or inorganic bodies, and more frequently to the former than to the latter. Most of the species of Sealpellans are inhabitants of deep water; on the other hand most of Pollicino, of Ala, and of Lithotryn are littoral forms. The species of bilhotryn have the power of excavating burrows in calcareous rocks, shells, and corals ; and the singular manner in which this is effected is described in Mr. Darwin'a work. Anelasma has its sub-globular podnncle deeply imbedded in the flesh of northern sharks, and instances have occurred of the beard end of the peduncle of Concha derma aurita being sunk into the skin of Cetacea; in the same way the point of the peduncle in the male of Ma is generally deeply embedded in the sac of the female. In all these cases the cementing sub stance affects and injures the corium or true skin of the animal on which the creature is parasitic, while the surrounding parts being not injured continue to grow upwards, thus causing the partial embedment of the Cirripede. In the case of we have growth at the end of the peduncle, and consequently downward pressure, and this may possibly cause absorption to take place in the skin of the shark at the spot pressed on.