37 
the summer months and up to the end of October, but the 
present season has been unusually mild, and Capt. Winslow, 
TJ. S. 17., tells me that he found oysters in October of this year 
in Tangier Sound, the eggs from which he succeeded in fertiliz- 
ing. It is possible, then, that those which I examined were 
ready to spawn this season. If this is so, all my observations 
have been made during the breeding season, and it may be pos- 
sible that later in the year hermaphrodite individuals may be 
found. There is nothing improbable in the statement that 
oysters change their sex, and that an individual may be a 
female one year and a male another year, but my observations 
certainly do not indicate that this is the case with the Ameri- 
can species. 
The only observations which I have met with on this sub- 
ject, made in this country, are by McCrady (Observations on 
the Food and Reproductive Organs of Ostrea Yirginiana, 
with some Account of Bucephalus Cuculus : Proceedings Bos- 
ton Soc. Hat. Hist., December 3d, 1873, pp. 170-192). He 
says that at a time when the ovarian eggs are very small and 
immature a the spermatozoa may be seen in their aggregated 
or even their free condition, actively moving about among 
masses of granular yolk substance, inclosing many germina- 
tive vesicles, without exhibiting any attraction for them, and 
without the appearance of any change in the young vesicles 
themselves.” (Page 172.) 
Regarding the oysters nearer the breeding season, when the 
eggs were more mature, he says, p. 174 : “ I endeavored next 
to ascertain whether or not spermatozoa were present, but 
•oould not satisfy myself on this point, as my eye had become 
fatigued, and no disposition of the light enabled me to dis- 
cover whether the minute dancing cellules, which were quite 
numerous, had or had not a tail.” 
This observation would seem to indicate that, while the 
sexual elements are immature, both male and female elements 
may occur in the same individual. 
The most thorough and satisfactory observations upon the 
sex of the European oyster are those by Mobius, and his 
account shows that the sexes are separate at the breeding 
