18 



G. O. SARS. 



[No. 8. 



the two sexes. The ovaries of the female (see PI. Ill, fig. 11) 

 are found between the two lamellae of either valve as an elon- 

 gate sac-like body, running from the central part of the shell 

 diagonally to the posterior extremity, immediately above the 

 coecal appendage of the intestine. On reaching the extremity 

 of the valve the ovarian sac curves upwards and forwards for- 

 ming a nearly semicircular bend. In this outmost part of the 

 ovary the true germinal layer is found, constituting an assemb- 

 lage of numerous very small and pellucid cellules, each pro- 

 vided with a very distinct and highly refracting nucleus. These 

 cellules become sucesssively larger and more distinctly defined 

 inwards, and soon form only a single layer containing at first 

 4, then 3, and at last only 2 juxtaposed cells of a polygonal 

 form, each with a very distinct nucleus, or germinal vesicle, in 

 the interior of which an equally distinct central body — the 

 germinal spot — is observed. In the inner part of the ovary, 

 finally, lying at the middle of the valve, there is only found a 

 single series of very large ovicells, the germinal vesicle of which 

 successively becomes quite hidden by an opaque, granular 

 matter — the vitelline mass — , accumulating in the interior. 

 The innermost of these ovicells is constantly the largest and is 

 ready to be poured off from the ovary. It soon becomes introdu- 

 ced within the body-cavity, and successively other ovicells 

 follow. They are however not yet ready to be deposited, 

 but still remain some time within the body of the parent, gene- 

 rally accumulating in its posterior part to either side of the di- 

 lated part of the intestine (see fig. 10). After having attained 

 their full development and having been fertilized, they are suc- 

 cessively deposited by the animal on foreign objects, and by the 

 aid of some secreting fluid glued together in rows or greater 

 masses. The openings, through which the ova are poured off, 

 would seem to lie on the inner side of the genital lobes, but their 

 exact place I have not been enabled to ascertain. As belon- 

 ging to the genital apparatus of the female may, moreover, he 

 mentioned a pair of rather large, elongate pyriform sacs (fig- 1° r ) 

 extending anteriorly beneath the intestine and generally filled up 



