62 



one other species of Cardium — 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 Laniellibranclies. 

 Annates des Sciences Nat. Ser. VI., t. II., Zool., pp. 153—248, PL V.— 

 IX., 1854. 



