160 



HELMINTHOZOA. 



dilated terminal receptacle common to both oviducts (I), from which 

 they are ultimately expelled. 



(427.) The attenuated commencements of the genital tubes in the 

 female Ascaris may be considered as representing the ovary, wherein 

 may be discovered numerous small round cells, which, as they advance 

 forward, begin to be surrounded with a granular vitelline substance, 

 wherein the primitive nucleated cells are still visible : these cells, there- 

 fore, ought perhaps to be regarded as germinal vesicles. Still further 

 onward the eggs are of a discoidal shape, and are arranged in a row, or 

 are grouped closely around a rachis that traverses the axis of the ovary. 

 In that portion of the genital canal which may be considered as repre- 

 senting the Fallopian tube the ova become more mature, and subse- 

 quently, surrounded by a double colourless envelope, pass into the base of 

 the uterus. This last is the widest portion of the genital tubes, and is 

 distinguished in the living animal by its well-marked peristaltic action. 

 The vagina, distinguishable from the uterus by its narrowness and its 

 muscular walls, opens into the vulva a narrow transverse fissure, some- 

 times surrounded by a very remarkable fleshy swelling, generally situ- 

 ated either in front of or near the middle of the body, but in some cases 

 in the vicinity of the anus. The sperm is usually accumulated in the 

 bottom of the uterus to such an extent as to render it probable that this 

 is the locality where the fecundation of the ova takes place*. 



(428). 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 fila- 

 ment (fig. 78, 2,/), which, when unravelled, is found to be nearly 3 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 filamentary retractile penis, 

 i, in which the microscope 

 exhibits a minute receptacle, 

 wherein the seminal fluid ac- 

 cumulates preparatory to its 

 expulsion. During copulation 

 the penis of the male is intro- 

 duced into the vulva of the 

 female, by which it is firmly 

 embraced, and the different 

 positions which the external 



Fig. 79. 



Trichina spiralis. 



parts occupy in the two sexes is evidently an arrangement favourable 

 to their intercourse. 



* Siebold, loc. cit. 



