'.: ' 



CIRRIPEDIA. 



CIRRIPEDIA. 



1 1 01 



the observation of the mean* by which them animal* attach 

 thrrasclvc* after leading a free life we are al*> indebted to Mr. Dar- 

 win. In the burn, two duct*, called cement-duct*, can be traced from 

 within the disc* of the antennio to the anterior or lower end* of the 

 two gut-formed bodies, which are the incipient ovaries. Them ducts 

 are filled with an opaque cellular nmttor in the larva, In the mature 

 ('impede*, they can be followed in a slightly sinuous course along the 

 muscles on each side within the peduncle, till they expand into two 

 mall organ*, which Mr. Darwin call* cement-glands. These glandn 

 contain a irtrongly coherent pulpy opaque cellular mass, like that in 

 the oement'ducta ; but in some instance* this cellular mass becomes 

 converted, within cither the ducts or gland, or within both, into a 

 transparent tough yellow cement Tubes are seen running into these 

 glands, containing ova in every stage of development. From obser- 

 vations made on many species of Cirripedes, Mr. Darwin concludes 

 that the gland itself is part of an ovarian tube specially modified ; and 

 further that the cellular matter, which in the ovarian tubes serves for 

 the development of the ova, is, by the special action of the walls of 

 the gland, changed into the opaque cellular matter in the ducts, and 

 this again subsequently into that tissue or substance which cement*. 

 the Cirripede to its surface of attachment. As the individuals grow 

 and increase in size, so do the glands and cement-ducts ; but it often 

 happens that when a specimen is immoveably attached, the cement- 

 apparatus ceases to act, and the cellular contents of the duct become 

 converted into a thread of transparent cement. The cement removed 

 from the outside of a Cirripede consists of a thin layer of very tough 

 bright-brown transparent laminated substance, exhibiting no structure 

 under the microscope. Its chemical reactions ore those of Chitine. In 

 the larva, the cement always escapes through the prehensile antennas 

 and in most instances it continues to do this throughout the life of 

 the animal. There are however exceptions, and in Scalpellum . 

 and probably others which live attached to coral, the cement soon 

 ceases to debouch from the antenna;, but instead bursts through a 

 row of orifices on the rostral margin of the peduncle, by which means 

 this margin is symmetrically fastened down to the delicate horny 

 branches of the zoophyte. 



The external shell, which misled early observers, and induced them 

 to place the Cirripedes among the JfoUiuca, is called, in the Lepadida, 

 the Capitulum. It is usually much flattened, but sometimes broadly 

 oval in section. It is generally formed of five or more valves, connected 

 together by very narrow or broad strips of membrane. When the valves 

 are numerous, and they sometimes exceed a hundred in number, they 

 are arranged in whorls, with each valve generally so placed as to cover 

 the interval between the two valves above. The upper pair of valves, the 

 peduncle being beneath, are called by Mr. Darwin the terga ; the pair 

 below it, on the same side, the taUa. The upper mesial valve opposed 

 to the two terga is the carina, and below this the tabcarina; and on the 

 opposite side again the rottrum. Below this is sometimes a subrostrum. 

 Of all the valves the scuta are the most permanent ; then come the terga, 

 and then the carina. The others occur only occasionally. The shell is 

 generally white, occasionally reddish or purple ; exteriorly the valves 

 are covered by more or less persistent, generally yellow, strong mem- 

 brane. The scuta and terga are always considerably larger than the 

 other valves. The adductor muscle is always attached to a point not 

 far from the middle of each scutum, which generally has a pit for its 

 attachment. The valves are cither placed close together or at some dis- 

 tance. The membrane connecting the valves, where they do not touch, 

 is like that forming the peduncle, and is sometimes coloured brilliantly 

 crimson-red; generally it is bluish-gray. Within the capitulum is 

 the sac, which, together with the upper internal part of the peduncle, 

 incloses the animal's body. 



The Peduncle varies in length in different species, and even in the 

 same species, according to the situation occupied by the individual. 

 It ia usually flattened, but sometimes quite cylindrical. It is com- 

 posed of very strong generally thick transparent membrane, rarely 

 coloured reddish, and often penetrated by numerous tubuli. The 

 peduncle is lined within by thin layers of muscles, longitudinal, 

 transverse, and oblique, all destitute of the transverse strise charac- 

 teristic of voluntary muscle*. They run from the bottom of the 

 peduncle to the base of the capitulum, as in Lrpm, or half way up it, as 

 in Conchmlrrma. The gentle swaying to and fro movement* and the 

 power of longitudinal contraction are produced by these muscles. 

 The interior of the peduncle is filled up with a great mass of branching 

 ovarian tubes. 



There are six pairs of cirri. The five posterior pairs are seated close 

 to each other and equidistant ; the first pair in generally seated at a 

 little distance and sometimes at a considerable distance from the 

 second pair. The first pair is shortest ; the others, proceeding back- 

 ward*, increase gradually in length. The number of segments in the 

 posterior cirri is very great The cirri are covered with spines. Most 

 of the genera have caudal appendages. 



The alimentary canal consists of an (esophagus, a stomach, and 

 rectum. The oMophagus is of considerable length ; it is formed of 

 strong transparent much-folded membrane, continuous with the outer 

 integuments, and moulted with them. At its lower end it expands 

 into a bell with the edges reflexed. This bell lies within the stomach, 

 and keeps the upper broad end expanded. The stomach lies in a 

 much-curved almost doubled course, and is often a little constricted 



where most bent It is broadest at the u|.|- r .-ml. The stomach 

 is coated by small opaque pulpy '-orescent glands, 



believed to be hepatic. The rectum varies in length . 

 inward* from the anus to between the bases of the sec..: 



irri. It in narrow, un.l I'.., ,1 ,,f i,m,-]i-r..l,l,..l I 



membrane. Within the stomach there can generally be seen, a 



ing to the period of digestion, a thin yet strong perfectly transparent 



epithelial membrane, not exhibiting under the microscope any 



ture. It enters the branching coco, and extend" from the n\g>- ot tlm 



bell of the oesophagus to the commencement of the closed rectu: 



was this membrane which was supposed by M. Mai '.nge to 



be a distinct organ, like the closed tube of certain A nnrlid<r. 



The circulatory system is not highly developed. No heart has been 

 discovered. The whole body is permeated by channels which have no 

 proper coat 



In most genera of the Lepadida; the nervous system consists of six 

 main ganglia, namely, the supra-coaophageal and five thoracic ). 

 Of these the first thoracic or infra-cosophageal ganglion -is . 

 the largest and most massive. It is squarish, or oval, or h..,i 

 presents no trace of being formed of two lateral ganglia. Two great 

 nerves spring from its under side, and mn straight down amongst the 

 viscera. These nerves are about as large as those forming the collar 

 and those running to the second ganglion ; hence six 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 

 organs. The muscles of the capitulum are supplied from the supra- 

 ocsophageal ganglion. 



Diagram of the anterior portion of the nervous system in Lefaifatcieularit. 

 A, flret thoracic or infra-rcsophageal ganglion ; D, second thoracic ganglion ; 

 C, third thoracic (fang-lion; D, Bupra-CBgophgeal ganglion; /;, t 

 ophthalmic ganglia ; F, double eye ; a, nerve going to first cirrhus ; 4, to the 

 muscles below the first cirrhus ; r, to the second cirrhux ; <1, In the third ; 

 t, nerves running to the ovaria; /, double nerves supplying the sac and 

 peduncle. 



Nerves proceed from the Bupra-oosophageal to the double eye of 

 Lepat fuucicuturii. The idea that the whole peduncle and capitulum 

 consist* of the first three segments of the hea.l i.- In autit'ully .-up- 

 ported by the structure of the nervous system, in which these parts 

 are seen to be supplied with nerves exclusively from the supra- 

 tcsophageal ganglion. In ordinary Cnutacea the supra-oosophageal 

 ganglion sends nerves to the eyes and the two pairs of nn 

 corresponding to the first three segments of the body. 



The reproductive system of the Cirripedes has excited much ir 

 from the result* of the researches of Mr. Darwin. All the Cirripedes, 

 with few exceptions, are bi-sexual, but Mr. Darwin has found tli 

 masculine power of certain hermaphrodite species of Ibla an< I 

 pellum is rendered more efficient by certain parasitic males, whieh, 

 from their not pairing, as in all hitherto known coses, with females, 

 but with hermaphrodites, Mr. Darwin designates Compleii 

 Males. The ordinary male organs consist of pear- or finger-shaped 

 bodies of a leaden colour, which coat the stomach, enter the pi 

 and even the basal segments of the rami of the cirri, and in some 

 genera occupy certain swellings on the thorax and prosoma. 



With regard to the ovaria, M unt-Angc has dew-rii-.l h..w 



the peduncle is gorged with an inextricable moss of branching ovarian 

 tubes filled with granular matter and immature ova. The ova when 

 excluded remain in the sac of the animal until the larva; ore hntrli. .1. 

 They are very numerous, and x< '"' 'rally form two concave nearly 

 circular leaves, called by Darwin Ovigerous Lamella;. The ova lie in a 

 layer, from two to four deep, and all are held together by a most 

 delicate transparent membrane, which separately enfolds each ovum. 

 This membrane is often thicker and stronger round the margins of 

 the lamelbe, where they are united in a peculiar manner, presently to 



