242 



THE LAMELL1BRANCHIA 



however, the male and female portions of the gonad are not actually 

 contiguous, but are united by a short canal (Fig. 218, t, ov), so that the 

 spermatozoa have to pass through the ovarian cavity before they are 



FIG. 210. 



Lyonsia norvegica, left-side view after removal of left pallial lobe and left gill, a, anus ; a.a, 

 anterior adductor ; a.s, anal siphon ; b.o, bysaal orifice ; br.n, branchial nerve ; br.s, branchial 

 siphon ; f.o, female orifice ; g, gill (direct internal lamina) ; g', reflected internal lamina of 

 the right gill ; g", outer plate of the gill ; l.p, labial palp.; m.o, male orifice ; o, ovary ; p.a, 

 posterior adductor ; p.o, pedal orifice of the mantle ; t, testis ; v.g, visceral ganglion. 



eliminated. Finally, in the fourth mode, an ovary and a testis com- 

 pletely separated from one another exist on either side of the body, 

 each having its own proper duct and external orifice. This is the 

 case in all the genera forming the order Anatinacea and in Poromya 

 among the Septibrarichia. In these forms the ovary is dorsal and 

 , posterior, the testis more anterior 



and ventral (Fig. 219, t.o). The 

 male and female genital orifices of 

 the same side are contiguous ; they 

 open on a common papilla in the 

 Anatinacea, but the female aper- 

 ture is outside the visceral commis- 

 sure, and therefore in the normal 

 and original position of the Lamelli- 

 branch genital orifice, whereas the 

 male aperture is within the visceral 

 commissure. In Poromya the male 

 and female ducts of each side open 

 into a common orifice, external to 

 the visceral commissure. In all 

 these hermaphrodites the male 

 products are the first to ripen. 

 Accidental cases of hermaphro- 

 ditism have been met with in 

 dioecious Lamellibranchs (Mytihis, 

 Unionidae), and a unisexual individual of the normally hermaphro- 

 dite species Pecten rjlaber has also- been described. 



FIG. 220. 



Pseudokellya mrilij'oiinis, section of a part 

 of the ovary, ce.f, follicular cells ; fol, ovular 

 follicle ; ov, ovarian egg. 



