THE CELL-STRUCTURE OF THE OYSTER. 721 



hermaphrodite. The male cells are so small compared with the eggs that it would be impossible 

 to state that a mass of eggs taken from the ovary contained no spermatozoa, although they could 

 not escape detection if they were at all abundant. 



"On the other hand, a single egg in the field of the microscope, in a drop of male fluid, would 

 be very conspicuous and could not escape detection; and the fact that not a single case of this 

 kind occurred is sufficient to establish the distinctness of the sexes at the breeding season."' 



Writing about this matter in 1880, I said : "No evidence to show that our Oyster is her- 

 maphrodite was found during the entire season ; nor were my searches for embryo or eggs in 

 the mantle or in the gills more successful than those carried on two years before by Professor 

 Brooks. There is no doubt whatever that the Oyster of Europe nurses its young in its mantle 

 or gills for some time; nor can wo well question the very high authority of Mobius for saying 

 that in most eases the sexes are separate, and that only one kind of products, viz, either eggs or 

 spermatozoa, are at any time found in the generative organs. Lacaze-Duthier's observations seem 

 to confirm the conclusions of Mobius." 



In reference to the structure of the cells which make up the body of the Oyster, as well as 

 regarding the eggs, Dr. Brooks, on page 19 of his essay, writes as follows: 



"Each of these consists of a layer of protoplasm around a central nucleus, which, in the egg, 

 is a large, circular, transparent body known as the germinative vesicle. Each cell of the body is 

 able to absorb food, to grow and to multiply by division, and thus to contribute to the growth of 

 the organ of which it forms a part. The ovarian eggs are simply the cells of an organ of the body, 

 the ovary, and they differ from the ordinary cells only in being much larger and more distinct 

 from each other ; and they have the power, when detached from the body, of growing and dividing 

 up into cells, which shall shape themselves into a new organism like that from whose body the 

 egg came. Most of the steps in this wonderful process may be watched under the microscope, 

 and owing to the ease with which the eggs of the Oyster may be obtained, this is a very good egg 

 to study." 



Brooks has represented the freshly laid ova of the Oyster with a spherical nucleus and 

 nneleolus ; the former is large and clear, and is imbedded near the center of the egg, and inside of 

 it the nucleolus is lodged somewhat to one side. I do not find the latter spherical, as described, 

 but formed as if composed of a larger and smaller highly refringent pair of spheres, partly fused 

 with each other, or of the same form as the nucleoli of the eggs of Anodonta as described by 

 Flemming. 



Some investigations conducted under the auspices of the Dutch Government indicate that the 

 structure of the generative organs of the European Oyster is not, as has been supposed, strictly 

 follicular, but that they may rather be regarded as a mass of anastomosing tubes of irregular caliber. 

 The complete proof of this has been developed by the writer in the course of investigations carried 

 out upon our native Oysters, in which the- generative organs were very immature during the 

 winter season. Both Brooks and myself have spoken of the generative follicles as though they 

 had been clearly made out; it now appears that we will be compelled to modify our terminology 

 somewhat, in the face of the fact that I have sections of the immature generative organ which 

 exhibit it as a network of germinal cells, as well as sections of the mature organs which show a 

 more or less distinct tubular structure opening toward the surface into the superficial or surface 

 outgoing canals. At the same time the tubes show more or less extensive junction or anastomosis 

 with each other at certain points along their length, with a general tendency to be disposed 

 vertically to the surface of the visceral mass. This arrangement reminds one somewhat of the 



'W. K. BROOKS: op. tit., p. 35. 

 4GP 



