106 CCELELMINTHA. 



terminal receptacle common to both oviducts (/), from which they 

 are ultimately expelled. 



(143.) The male Ascaris lumbricoides is considerably smaller than 

 the female, and the. structure of its generative system remarkably 

 similar to what has been just described in the other sex. The testis 

 or gland, which secretes the impregnating fluid, is a single, delicate, 

 tubular, filament (fig. 44, 2,jf), which when unravelled is found 

 to be nearly three feet in length, and is seen winding in close and 

 almost inextricable folds around the middle and hinder parts of 

 the intestine. The termination of this tube (g) may be traced to 

 the tail or anal extremity of the worm, where it ends in a fila- 

 mentary retractile penis (z), in which the microscope exhibits a 

 minute receptacle wherein the seminal fluid accumulates prepara- 

 tory to its expulsion. During copulation, the penis of the male 

 is introduced into the vulva of the female, by which it is firmly 

 embraced, and the different positions which the external parts 

 occupy in the two sexes is evidently an arrangement favourable 

 to their intercourse. 



(144.) There are few more striking exemplifications of that gra- 

 dual transition by which we are led from one type of structure to 

 another, than we meet with in tracing the progressive separation 

 of the sexes as we advance from the monoecious to the dioecious 

 families of the entozoa. Leaving those forms of hermaphroditism 

 in which the male and female parts are both found in each division 

 of the body, we find in Syngamus trachealis an animal " in which 

 the male is organically blended by its caudal extremity with the 

 female, immediately anterior to the slit-shaped aperture of the 

 vulva, which is situated as usual near the anterior third of the 

 body. By this union a kind of hermaphroditism is produced ; 

 but the male apparatus is furnished with its own peculiar nutrient 

 system, and an individual is constituted distinct in every respect, 

 save in its terminal confluence with the body of the female. This 

 condition of animal life, which was conceived by Hunter as within 

 the circle of physiological possibilities, (see Animal (Economy, 

 p. 46,) has hitherto been only exemplified in this single species 

 of entozoon, the discovery and true nature of which is due to 

 the sagacity and patient research of Dr. Charles Theodore Von 

 Siebold."* 



* Cyclop, of Anat. and Phys. ; article Entozoa, by Professor Owen. Vide Siebold, 

 in Weigmann's Archives, 1835. 



