SEA-FISHERIES LABORATORY. 939 
one other species of Carditwm—C. serratum (=C. nor- 
vegicum), investigated by Lacaze-Duthiers,* the animal 
is hermaphrodite; on the same branch duct alveoli are 
present, some of which are filled with ova, some with 
spermatozoa; and both genital products may be found 
even in the same alveolus. In the edible cockle there is | 
little difference between the gonads of different sexes apart 
from their contents. The male gonad is less voluminous 
and more opaque. 
In the animal taken during the spring or early summer 
the gonad is nearly filled with ova or spermatozoa, as the 
case may be. In a transverse section through an alveolus 
of the male gland (fig. 39, Pl. VI.) there is a peripheral 
zone of small, dense cells lying close to, and obscuring the 
wall. Where the latter can be observed it is seen to 
consist of a single layer of small, rounded cells supported 
on a delicate basement membrane. Within this is the 
zone of cells referred to, which results from the pro- 
liferation of the germinal epithelium forming the wall. 
Towards the centre of the alveolus these become smaller 
and denser as they become transformed into the mature 
spermatozoa. The elongated head pieces of the latter are 
arranged in radial streaks converging towards a portion of 
the wall, which does not consist of germinal epithelium, 
and where there is generally a slight space. The long tail 
pieces are directed towards this space and alternate with 
the rows of heads. In the alveoli this part of the wall, 
towards which the streaks of spermatozoa converge, is thin 
and presents no particular structure. In the larger ducts, 
however, it consists of a strip of ciliated epithelium where 
the cells are irregular and have clear cell contents. In 
*Recherches sur les organes genitaux des acephales Lamellibranches 
Annales des Sciences Nat. Ser. VI., t. II., Zool., pp. 153—248, Pl. V.— 
DX; 1854, 
