690 



CIRRHOPODA. 



the mantle. Professor Burmeister describes 

 the gills of Coronula diadema as broad mem- 

 branous expansions, of a semicircular form, 

 attached to the sides of the visceral mass by a 

 narrow pedicle. They are composed of two 

 tunics arranged in deep and narrow transverse 

 plaits. The number of the branchiae in the 

 Lepads varies from four to sixteen. They are 

 composed of soft cellular tissue, and have a 

 smooth surface. 



The arms (h, h, Jig. 340), which constitute 

 so large a portion of the general mass of all the 

 Cirripeds, and which form their most distinc- 

 tive feature, must be regarded as subservient 

 chiefly to the function of respiration; although, 

 by producing currents in the water, which 

 bring food within reach of the jaws, they minis- 

 ter also to the digestive function. In all the 

 known species, both of Lepads and Balanids, 

 these arms are twelve in number, six on either 

 side, arranged symmetrically. Each arm is 

 composed of a short fleshy peduncle, having 

 three articulations, and two horny articulated 

 processes, compressed laterally, of equal length, 

 ciliated on their internal surfaces, and coiled 

 up in a spiral of one turn. On their internal 

 surface there is a coating of a black pigment in 

 spots. Each joint is provided with a double 

 row of hairs of different lengths. (Fig. 343.) 



Fig. 343. 



A part of one of the arms considerably magnified. 



In Anatifa, the first pair of arms is thicker and 

 stronger than the others ; the sixth pair is the 

 longest. Dr. Grant says, " the arms are not 

 only minutely jointed to their extreme points, 

 but, also, the innumerable fine cilia which pro- 

 ject inwards from their surface are themselves 

 minutely jointed, and by the aid of the micro- 

 scope, we can perceive that these jointed cilia 

 are also ciliated on their margins." 



When the animal is at rest, with the valves 

 of the shell closed, the arms are coiled up, and 

 lie close to one another; but, at other times, 

 circumstances being favourable to the perform- 

 ance of the function of respiration, they are ex- 

 tended simultaneously so as to project from the 

 shell, radiate and plumose in their arrange- 

 ment. Many species extend and contract their 

 arms with considerable rapidity, as often as 

 forty or sixty times in a minute ; the smaller 

 species more frequently than the larger. 



Considering how extensive the surface is 

 which is exposed in the arms between the two 

 rows of cilia, and that a vessel seems to run 

 immediately beneath the delicate covering of 

 these organs in that situation, it appears proba- 

 ble that the arms are very efficient agents in the 

 function of respiration. 



Secretion. We have failed to ascertain satis- 



factorily the structure of the secreting apparatus 

 by which the shells of the Cirripeds are formed. 

 In the Lepads, the organs must be imbedded 

 in the ligamentous membrane by which the 

 valves are united : and in the Balanids, they are 

 arranged in six rows along the outer surface of 

 the mantle, and around the base; but, as in 

 acephalous mollusca, they are too small to ad- 

 mit of their structure being particularly exa- 

 mined. The external surface of the mantle in 

 the Balanids has also the power of secreting 

 calcareous matter, with which to increase the 

 thickness of the shell. 



Reproduction. It is not yet accurately de- 

 termined what are the organs of reproduction 

 in these animals. That which was regarded by 

 Cuvier as the ovary in the Lepads, is supposed 

 by Professor Wagner and M. St. Ange to be 

 the testicle ; while Professor Burmeister has 

 satisfied himself that it is the liver. The ex- 

 tent, structure, and relations of the ovary are 

 still doubtful. It is certain, however, that all 

 the known Cirripeds are hermaphrodite. 



The testicle, according to Professor Wagner 

 and M. St. Ange, is a large granular organ 

 (y, Jig. 344), expanded over the sides of the 



Fig. 344. 



visceral mass, and around the digestive canal, 

 from the stomach to the anus, passing even into 

 the bases of the arms, immediately beneath the 

 muscular tunics which cover the body on both 

 sides. It is composed of numerous minute 

 lobules, about 3 igth of an inch in diameter iu 

 the common Lepads, soft, white, grouped toge- 

 ther by branched ducts ( </, q, Jig. 344), which, 

 after uniting into three or four principal trunks,* 

 meet in a large central receptacle (r), some- 

 what analogous in relative function to the vas 

 deferens of vertebrate animals. The seminal 

 fluid passes from this central receptacle by a 

 short and straight duct into a large canal (t, t), 

 which may be compared to the seminal vesicle. 

 It pursues a tortuous course towards the base 

 of the tubular process, where (/c) it is joined by 

 its fellow of the other side, and enters the canal 



* This description does not accord with the result 

 of Protessor Burmeister's researches. Instead of 

 a regular series of hranched vessels, he says that 

 he met with nothing but an irregularly arranged 

 mesh of thready fibres lying between what he be- 

 lieved to be the liver (described above as the testi- 

 cle) and the intestinal canal. 



