BULLETIN OF THE UNITED STATES FISH COMMISSION. 205 



rived from the same parent. I might cite facts to show that a single 

 laying of eggs may produce individuals which differ from each other in 

 many minor details j this variability is very marked in the plumage of 

 broods of domestic birds, and I am informed by Mr. T. R. Peale that 

 he has met with remarkable instances amongst butterflies, broods of 

 which he had reared artificially from the eggs of a single parent. These 

 well-known facts indicate that still another principle should not be lost 

 sight of; namely, that the hidden constitutions of different germs of the 

 same parent are variable ; that the living matter of the germ-producing 

 organs themselves is not similar in its developmental tendencies. It 

 follows from this, that when I say that in the protoplasm of the shad 

 there inhere specific properties which are transferred to and embodied 

 in its germs, I do not mean to say that the living matter of all parts of 

 the body is alike, but that the protoplasm of its parts when compared 

 with the same parts of other species must be unlike the latter. To put 

 the same idea in other phraseology, I would say that not only is the pro- 

 toplasm of the species specific, but also that, if we consider the* facts of 

 variation, the different as well as the same parts of the body of one and 

 the same species must be variable in their hidden and transmissible con- 

 stitutions. In following out such a train of thought, it is almost im- 

 possible not to trench upon Darwin's Hypothesis of Pangenesis, as we 

 have done above ; but it is to be borne in mind, if one is faithful to the 

 showings of right reason, that it is scarcely possible to escape such a 

 coincidence. 



THE MICROSCOPIC SEXUAL CHARACTERISTICS OF THE AMERI- 

 CAN, PORTUGUESE, AND COMMON EDIBLE OYSTER OF EUROPE 

 COMPARED. 



By JOHN A. RYDER. 



In the issue of Forest and Stream of November 30, just past, in an 

 article by the writer, page 351, middle column, it is remarked : " I re- 

 gard Davaine's observations upon the histology of the reproductive or- 

 gans [of the European oyster] as of little value, being made before the 

 introduction of improved methods of investigation. His figures of the 

 finer structural details have apparently been made from crushed frag- 

 ments.". In passing this judgment upon Dr. Davaine's work, I have 

 been severer than the state of the case demanded, as will be seen in the 

 sequel, though I do not yet admit that his methods of research were 

 what they should have been, for until now we have had no adequate de- 

 scription of the structures in question. Until recently I have maintained 

 with reservations that the sexes in the European oyster were probably 

 separate as in the American ; more recent investigation with more 

 refined methods have proved to me that in this I am in error. In my 

 article in Forest and Stream I also took occasion to refer to a statement 

 in Gegenbaur's Elements of Comparative Anatomy, English edition, p. 



