206 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



380, where lie says : " In the oysters we find an intermediate step toward 

 a separation of the sexes, inasmuch as these organs are not active at 

 the same time in the same individual ; but the male and female organs 

 alternately so." The writer in commenting upon the above then wrote : 

 " This quotation tacitly admits the unisexuality of the European oyster 

 to which it evidently refers. The last part of the remark, however, is 

 founded upon the slenderest kind of evidence ; in fact, upon no evidence 

 except a surmise, as such an alternate activity of the two parts is im- 

 probable [for obvious reasons]; besides, it is not possible to demonstrate 

 such an alternation of sexual activity in the same individual. As every 

 one knows, the soft parts of an oyster cannot be examined without open- 

 ing the shell, which necessarily makes the needed second observation to 

 confirm this alleged alternation of sexual activity a physical impossi- 

 bility." I am now in a position to go still further and to assert that the 

 first part of the quotation from Gegenbaur is also erroneous, because 

 we may # find both eggs and spermatozoa in the same follicle at the same 

 time. 



What, then, is the true state of the case % This query we propose an- 

 swering, but before we set out it will be necessary to give some account 

 of the methods of investigation used in order to arrive at a definite con- 

 clusion. Thin sections of those portions of the animal in which the 

 reproductive structures are lodged are of the first importance. After 

 trying various methods, which were found for the most part unsatisfac- 

 tory, the preparation of sections was finally conducted as follows : After 

 the soft parts were removed from the shell they were thrown into a 

 chromic acid solution of one to two per cent., in which they were al- 

 lowed to remain for several days, and in some cases the hardening solu- 

 tion was even renewed. This was done in order that the hardening 

 agent might act upon the whole of the soft parts and harden them 

 throughout ; unless the chromic acid is allowed some time to act upon 

 the entire animal it will not be uniformly hardened, the center of the 

 body remaining soft. After hardening, the animals should be thor- 

 oughly washed and soaked in water for a couple of days to remove all 

 traces of the acid before they are finally put into alcohol for permanent 

 preservation. Hardened material so preserved will make good sections 

 months afterwards. 



Portions of the body mass of different individuals should then be cut 

 out; it is best to cut up the body into thick slices or blocks in a trans- 

 verse direction, large enough to be conveniently held between the fin- 

 gers. It was also found advisable to take such thick slices of the hard- 

 ened body mass from several individuals, since it was discovered that 

 scarcely any two had the reproductive glands developed to exactly the 

 same degree of maturity. This point is important, as it has enabled us 

 to follow up the development of the reproductive organs in the connect- 

 ive tissue which invests them. After considerable experiment and dis- 

 appointment in the effort to imbed these thick, hardened slices so as to 



