MORPHOLOGY OF L AMELLIBRAN CHIATE MOLLUSKS. 
405 
In a majority of cases the sexes are separate, hut hermaphroditism exists in very 
many forms. Pelseneer points out the fact that it exists in isolated forms, species in 
certain genera, as in Ostrea , Pecten , and Gardium , and whole genera in certain families, 
as in the case of Gyclus , Pisidium , and Entovalva. He says : “ Chez tous ces animaux la 
glande genitale elle-meme est hermaphrodite; elleproduit dans toute son etendue des 
ceufs et des spermatozo'ides, ou bien si une partie est specialist pour donner naissance a 
chacun de ces produits, ceux-ci sont amenes au dehors par une seul canal, hermaphro- 
dite ( Pecten ).” 
The European oyster, Ostrea edulis , is hermaphrodite, but in the American form, 
0. virginiana, the sexes are separate. While rearing the young of this form from the 
eggs at Woods Holl, with Mr. Harrison of the Johns Hopkins University, we found a 
specimen apparently containing both eggs and spermatozoa. On sectioning parts of 
the generative gland, I found it to be hermaphrodite, as was suspected. The large 
follicles (Fig. 72, PI. lxxxix) were generally more or less united, and their lumens 
everywhere, in specimens taken from a number of different parts of the glands, ap- 
peared full of ripe spermatozoa. The ova, with their distinct nuclei, were apparently 
unripe, though many were free from the follicle walls. The majority of them were 
yet attached. The cells of the follicular epithelium showed ova in all stages of growth, 
and none of them, apparently, were giving rise to spermatozoa. 
This specimen was obtained late in June, near the end of the breeding season. 
Whether or not its sexual glands indicate the change in function from male to female 
or from female to male, which possibility has been suggested for some lamellibranchs, 
I can not say ; but, as abnormal hermaphroditism often occurs in all groups of animals, 
this may be an example of it. 
The sexual gland of Pecten irradians is hermaphrodite, and there are an ovary and 
a testis on each side of the visceral mass. Both glands are ventral to the liver (Fig. 
44, g ) and have a spongy appearance. The testis is the more ventral of the two and 
is of a cream color. The ovary, situated above this, has a reddish hue, which is very 
marked in the living animal. 
Fig. 71 represents a section passing vertically through the outer wall of the vis- 
ceral mass, where the testis and ovary are closely apposed. The body wall is repre- 
sented at ep and consists of a single layer of columnar, ciliated, epithelium cells, 
whose nuclei are about equally distant from their outer ends and the thick basement 
membrane ( bm ). In this epithelium are many conspicuous gland cells (glc). Be- 
tween it and the follicles of the generative gland is a thick layer of connective 
tissue, extending in between the follicles. The follicles of the ovary ( ov ) are not so 
regular in outline when seen in section as those of the testis ( t ). The walls of the 
latter bear a follicular epithelium ( fep ). In the ovary, the cells of this layer are in 
all stages of development into eggs. The eggs themselves, crowding the follicles, 
possess a very thick egg membrane and their protoplasm is finely granular. A duct 
from the follicles is seen at d. 
The mother cells of the spermatozoa (fep) are circular and of constant size in the 
follicles of the testis ( t ). As we follow the mass of cells inward from these mother 
cells they become very gradually smaller and smaller, until their final divisions result 
iu the spermatozoa. These are so arranged that their “tails,” in forming, project in 
extended masses toward the lumen of the follicle and give it a radiating appearance. 
