714 CLASS XII. 
Lamellibranchiata, perhaps hereafter external sexual difference 
will be looked for. In Anodonta, at least, the females may be 
recognised by their more convex shells’. However all Lamelli- 
branchiata are not of different sex; Pecten, for instance, according 
to Minne Epwarps, is hermaphroditic’; also in Cyclas, besides 
the ovaries, two testes are present®. 
The structure of the ovaries has, by the investigations of Pott, 
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 
eges 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 imner 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 Unio and Anodonta’. 
1 V. SIEBOLD op. cit. s. 391; KIRTLAND appears to have remarked this difference 
in Unio also. 
2 Ann. des Sc. Nat. 2e Série, XVIII. 1842, Zoologie, pp. 321, 322, Pl. 10, fig. 1. 
3 WaGNER found spermatozoa in all the individuals of Cyclas cordata which he 
investigated ; WIEGMANN’S Archiv, 1835, 11. s. 218, Tab. 111. fig. 8. The presence of 
two testes and two ovaria in genus Cyclas was observed by V. StEBOLD, MUELLER’S 
Archiv, 1837, 8. 383, 384. [See on the genital organs of Lamellibranchiata, H. LecazE- 
Dutuiers Ann. des Sc. Nat., Zool. 4ieme Série, Tom. I. pp. 155—248. 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. levigatwm 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 Pout Testac. utriusg. Sicil. 1. Tab. 1x. 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. Poxi and most observers have found 
the eggs in the external gills alone, Bosanus 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 conchifera 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 
