CRUSTACEA. 



783 



plete state of doubleness ; on either side of the 

 body we find an organ perfectly distinct, and 

 often wholly independent of its fellow ; to such 

 an extent, indeed, is this carried, that among 

 the facts with which modern science has been 

 enriched in regard to the structure of the Crus- 

 tacea, one by no means the least interesting is 

 that in which an animal of this class was actu- 

 ally found presenting in either half of its body a 

 different sex, each apparatus complete in every 

 one of its conditions, and even with the whole 

 of its modifications.* 



Another fact, not less striking, is that of the 

 analogy which exists, at least among the more 

 perfect Crustaceans, between the male and the 

 female reproductive organ. This similarity is 

 so great that the simple inspection of the organ 

 is not alone sufficient to inform us always of 

 its true nature, which in some instances can 

 only be ascertained by the most carefnl 

 examination. 



The male apparatus consists essentially of an 

 organ the secreting instrument of the fecunda- 

 ting fluid, and of an excretory canal variously 

 modified. These two parts are contained within 

 the thorax along with nearly the whole mass of 

 other viscera, and never extend lower down 

 than the last ring of this region of the body. 

 They are not always very distinct from one 

 another, and it frequently happens that the 

 testis and the excretory canal are confounded 

 inextricably under the form of a single tube, 

 nearly identical in its structure from beginning 

 to end. The length of this canal is occasionally 

 very great and variously convoluted and con- 

 torted, so that its relations with the other tho- 

 racic viscera become excessively multiplied. 

 This peculiarity we observe very well in the 

 Maja and the Cancer pagurus (see fig. 418). 

 The canal, which throughout is single, is 

 capillary at its commencement, but increases 

 gradually in its dimensions to its termina- 

 tion. 



In the Astacus fluviatilis, on the contrary, 

 the two portions of the male reproductive 

 apparatus are perfectly distinct, and severally 

 completely developed. The testis (a, fig. 432) 

 consists of capillary secerning vessels, which 

 are readily demonstrable, and presents three 

 lobes, two of which lie forwards upon the 

 sides of the stomach, and one backwards 

 underneath the heart. From these three lobes 

 two excretory canals (6) take their origin. In 

 the Edriophthalmia the male organ is com- 

 posed of two or three elongated vesicles, which 

 terminate in a common excretory canal. 



It is in the Cancer pagurus perhaps that the 

 male organ of generation is most highly de- 

 veloped. It occupies of itself a large por- 

 tion of the thorax (jig. 418). The testis pre- 

 sents the appearance of a kind of grape 

 cluster, formed of four principal lobes, which, 

 studied minutely, are found to be made 

 up of an infinity of extremely delicate ver- 

 micular canals, contorted so as to form great 

 numbers of pellets. This first portion of 



* An account of an Hermaphrodite Lobster, 

 by Dr. Nichols, Philos. Trans. 1730, p. 290. 



Fig. 432. 



e 



Male organs of the Astacus Fluviatilis. 



a, testis ; b, excretory ducts j c, terminal portion 

 of these ducts j d, orifice j e, last pair of ambu- 

 latory legs. 



the organ is situated in front of the thorax, 

 and terminates in a primary large convoluted 

 vessel lying on the side of the stomach ; be- 

 hind and in connexion with this we perceive 

 the vas deferens, properly so called; it is a 

 canal of considerable size, much convoluted, 

 and of a milky white colour; it traverses the 

 thorax, still twisting about, penetrates the cell 

 of the last pair of ambulatory extremities, and 

 opens outwardly on their basilar piece. This 

 indeed is the situation in which the copulatory 

 organs of the Crustacea generally appear. 

 Still, in many Brachyura of the Catometopa 

 family, the Ocypoda and Grapsus for ex- 

 ample, the external opening of the male gene- 

 rative organ is found on the sternal part of the 

 last thoracic ring ; and there are even several 

 of these animals in which the efferent canal, 

 after having attained the external surface in the 

 basilar articulation of the last pair of ambu- 

 latory extremities, returns inwards, and pene- 

 trates by a small groove, which conceals it 

 until it has attained to that portion of the 

 sternum which is hidden by the abdomen; 

 an example of this occurs in the Gonoplax. 

 In the ordinary state the excretory canal termi- 

 nates on the edges of the opening, but at the 

 instant of sexual intercourse the extremity of 

 the canal undergoes a kind of erection, and 

 by becoming folded upon itself like the finger 

 of a glove, projects externally, so as to forma 

 kind of penis adequate to the intromission of 

 the fecundating fluid. This latter circumstance 

 was long unknown to naturalists, who were 



