714 CLASS XII. 



Lamellibranchmta, perhaps hereafter external sexual difference 

 will be looked for. In Anodonta, at least, the females may be 

 recognised by their more convex shells 1 . However all Lamelli- 

 branchiata, are not of different sex ; Pecten, for instance, according 

 to MILNE EDWAKDS, is hermaphroditic 2 ; also in Cyclas, besides 

 the ovaries, two testes are present 3 . 



The structure of the ovaries has, by the investigations of POLI, 

 become known in many genera of Lamellibranchiata. The two 

 ovaries lie on each side of the intestinal canal and the liver, and 

 consist of tubes that divide into branches terminating blindly; 

 they have often a proper colour, ordinarily red or rose-red, by 

 which they are distinguished from the neighbouring parts. The 

 eggs pass from the ovary by an aperture situated on each side of 

 the foot or the abdomen, at the inside of the opening of the 

 vacuities in which the venous sinuses are contained. In the same 

 situation lie the apertures by which in the male conchifers the 

 sperma is evacuated. Afterwards the eggs proceed along the foot 

 into an opening between the foot and the inner gills, and arrive 

 at the canal of the inner gills, which conducts to the cloaca. From 

 here the eggs are carried to the lobes of the mantle, or they come 

 outward and are brought by the respiratory streams from behind 

 into the canal of the external gills, and deposited between the 

 plates in the saccules of these gills, as in Unto and Anodonta*. 



1 V. SIEBOLD op. cit. s. 391 ; KIRTLAND appears to have remarked this difference 

 in Unio also. 



2 Ann. des Sc. Nat. IQ Sdrie, xvm. 1842, Zoologle, pp. 321, 322, PI. 10, fig. i. 



3 WAGNER found spermatozoa in all the individuals of Cyclas cordata which he 

 investigated; WIEGMANN'S Archiv, 1835, II. s. 218, Tab. in. fig. 8. The presence of 

 two testes and two ovaria in genus Cyclas was observed by V. SIEBOLD, MUELLER'S 

 Archiv, 1837, s. 383, 384. [See on the genital organs of Lamellibranchiata, H. LECAZE- 

 DUTHIERS Ann. des Sc. Nat., Zool. 4'ieme Serie, Tom. n. .pp. 155248. He adds 

 Ostrea, so much contested, to the list of the hermaphrodites. Pecten, which is usually 

 bisexual, has one species (Pecten varius) unisexual, whilst Cardium, usually unisexual, 

 has Cardium serratum and Card. Icevigatum bisexual. In some hermaphrodites, the 

 sexual organs, though united in the body of the same animal, are quite distinct (Pecten, 

 &c.), in others they are quite confused, (Ostrea).'] 



4 The figure of POLI Testae, utriusq. Sicil. I. Tab. IX. fig. 18, gives a good idea of 

 these chambers formed by transverse septa, triangular and much elongated, which have 

 their bases turned to the dorsal side of the gills. POLI and most observers have found 

 the eggs in the external gills alone, BOJANUS occasionally found some in the internal 

 also. Thus the respiratory function is not prevented by these eggs ; but only partially 

 interrupted, and since there are many conchifcra in which the gills do not serve for the 

 reception of eggs, there is the less reason for refusing to these organs the function of 



