THE LAMELLIBRANCHIA 241 
into the kidney of the same side, not near the pericardial orifice, 
but nearer to the external aperture, ¢.g. in the Anomiidae and 
Pectinidae, or close to the external orifice, as in Arca. In other 
cases the gonad and the kidney open together into a common slit or 
cloaca (Ostraea, Cyclas, Fig. 218, g.0, and certain Lucinidae). Finally, 
in those cases in which there is a separate generative aperture, it 
may either be situated on a papilla common to it and to the renal 
orifice (Mytilus edulis), or, as is most frequently the case, it may be 
in the immediate neighbourhood of the renal orifice, and like it, 
situated to the outside of the visceral commissure (Fig. 242, (6) ). 
When normal hermaphroditism occurs in the Lamellibranchia, 
it may exist in one of the following different forms. In the first 
each gonad is entirely hermaphrodite throughout its extent; that 
Fia. 218. 
Cyclas, left-side view, after removal of the left pallial lobe, gill, and auricle. a.a, anterior 
adductor ; a.o, auriculo-ventricular orifice ; a.r, anterior foot retractor ; @.s,:anal siphon ; b7.s, 
branchial siphon; f, foot; g, right gill; g.o, genital orifice; im, intestine; k, left kidney; 7, 
liver ; ov, ovary ; p.a@, posterior adductor; p.r, posterior foot retractor ; t, testis; v, heart- 
ventricle ; v.g, visceral ganglion and commissure (posterior part). 
is to say, uniformly composed of acini capable of producing ova and 
spermatozoa simultaneously or successively. ‘This condition is 
found in Ostraea edulis, O. angasi, O. plicata, O. lwrida (other species 
of Ostraea, viz. O. virginica, O. glomerata, and O. angulata are 
dioecious), Kellya, and Lasaea. In the second form there are male 
and female acini lying side by side throughout the whole extent of 
the gonad, e.g. Tridacna, Cardiwm oblongum, and C. norvegicum. In 
the third form the gonads are differentiated into regions of different 
sex, the anterior region being male and the posterior female (Fig. 
235, t, ov), but these are not separate from one another, and have a 
common duct and a single orifice: this is the case in Pecten herma- 
phroditus, P. maximus, P. jacobaeus, P. opercularis, P. glaber, P. irra- 
dians, and P. flexuosus (P. inflecus and P. varius are dioecious). The 
same arrangement is found in the Cyrenidae (Cyclas, etc.), in which, 
16 
