BULLETIN OF THE UNITED STATES FISH COMMISSION. 213 



As to the alternate activity of the organs in producing ova and sperma- 

 tozoa there is a possibility that such is the case, but as stated at the outset 

 there is as yet no conclusive proof of the fact. Certain it is, that I have yet 

 to see sections of 0. edulis in which both ova and spermatozoa are not 

 present in some condition of development at the same time. If the one 

 be not present in a fully developed state, developing traces of it may be 

 •discovered, or even a very minute quantity of developed milt or a few 

 developed eggs may be present in some one follicle, while in the others 

 there are perhaps exclusively eggs or exclusively milt in a developed 

 condition. I am aware that this view of the matter is opposed to the 

 current doctrine that nature provides against continuous interbreeding, 

 but when we find the eggs and milt about equally advanced in develop- 

 ment in the same follicle, what is there to prevent self-fertilization ; iu 

 fact, what else can be the mode of reproduction ? 



In some of the sections of 0. edulis examined by me the ovules already 

 measured 257th of an inch in diameter, showing them to be about twice 

 ' the size of the ripe eggs of 0. virginica and 0. angulata, in both of which 

 the ova are of about the same size when mature. Estimates which I 

 have made, based on the figures of the eggs of 0. edulis given by M. 

 Davaine, show them to be ys oth of an inch in diameter. Estimates based 

 on the figures of Lacaze-Duthiers give 2 loth of an inch, while Mobius and 

 Horst give the size of the young fry at ylsth of an inch in diameter. The 

 spherical heads of the spermatozoa of the three species here discussed 

 measure about the same or approximately, yg-^o o^h of an inch in diam- 

 eter. The clusters of spermatozoa of 0. edulis measure approximately 

 T i^th of an inch in diameter. The spherical unsegmented spermato- 

 blasts which break up into spermatozoa in 0. edulis measure ysVoth 

 of an inch in diameter. The nucleus of the ovarian eggs of 0. edulis 

 measure not quite yioth of an inch in diameter. The nucleus of the 

 ovarian egg of 0. angulata measures approximately tsVs 1 ^ of an inch in 

 diameter, which is about that of the nucleus of the egg of 0. virginica. 

 The large spherule of the nucleolus of the egg of 0. edulis measures 2^5-oth 

 of an inch in diameter; the small spherule, which is stained red by the 

 safranin, measures TiVoth of an inch ; the long diameter of the conjoined 

 spherules is TrVoth of an inch. The long diameter of the nucleolus of 

 the egg of 0. angulata and 0. virginica is about ToVo^h of an inch. A 

 slide in my possession containing some of the brood of 0. edulis shows 

 that, even after it has acquired both valves of the shell within the beard 

 of the mother oyster, the brood varies greatly in size. I find, for example, 

 that such fry measures from -rhrth of an inch down to as small as yioth. 

 This brood, like that of the American oyster, has not yet acquired any 

 umbonal prominences at the hinge end of the valves. Before this occurs 

 in the American oyster embryo considerable growth has taken place, 

 but when the shell already covers the body the whole embryo, contrary 

 to what is found in the European species, measures little, if any, more in 

 diameter, than the egg, or about ^oth of an inch. Later, when the 



