406 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



are received from tlie canalicular structures in which tliey are matured. 

 At no time do we find the generative organs quite undeveloped. If they 

 are not apparent to the eye in winter, sections show the ducts and micro- 

 scopic rudiments of germinal follicles or tubules, as a net- work of strands 

 of minute germinal cells, which traverse in all directions the coarse 

 superficial layer of vesicular connective tissue cells, miscalled the "fat.'' 

 As the breeding season approaches, the minute germinal cells of this 

 net- work of rudimentary reproductive cells commence to grow until they 

 attain the development observed in the animal when full of spawn. The 

 ducts or follicles are never developed in the mantle, but the substance 

 of the latter may come into contact externally and superficially with the 

 generative organs. 



The terms "fry" and "spat" I have endeavored to use in such a way 

 as to avoid confusion. As soon as the egg has developed far enough to 

 move about by means of the fine motile filaments with which it is par- 

 tially covered, it may be considered to have reached the fry stage of 

 development, and to have hatched, but it is to be borne in mind that 

 an oyster egg does not hatch in the same sense as does the egg of a chick 

 or fish, that is, by breaking its egg shell or membrane, because the oys- 

 ter egg is without a membrane such as must be cast oft' in the act of hatch- 

 ing in the former cases. As soon as it has ceased to rove about in the 

 water, and has fiistened itself to some other object, it has attained the 

 stage of development known to oystermen by the term "spat." 



Our researches (see Maryland Eeport, 1881) show that the dimensioos 

 of the fry of the American oyster at the time it ceases to be "fry," fixes 

 itself, and becomes spat, is about one-eightieth of an inch, and at that 

 time the valves are characterized by a very remarkable symmetry, which 

 is departed from as soon as the growth of the sliell begins in its new 

 fixed position. The manner in which this attachment is made has not 

 been learned, but it is very probable that this is accomplished by means 

 of a larval bj'ssus. Such a conclusion appears to be warranted by the 

 fact that the larvte or swimming young of most of the allies of the oyster 

 are provided with a byssus or threads for their temporary anchorage, 

 such as may be seen very strongly developed in the adult salt-water 

 mussel. 



All theorization in regard to the nature of the mechanism of fixation 

 aside, however, it now becomes a question of the most profound impor- 

 tance for us to endeavor by experiment to maintain artificially impreg- 

 nated oyster eggs alive for a long enough time after they begin to swim, 

 so that they may have an opportunity to attach themselves. The experi- 

 ments of those who have hitherto worked ux)ou the dovelopment of the 

 oyster have shown us that this is exceedingly difiicult to do, and that be- 

 yond the present stage of our knowledge and experience much still re- 

 mains to be achieved. Various forms of apparatus have been tried with 

 indifterent success. The exjjeriment of using bibulous paper diaphragms 

 through which the sea- water was allowed to pass was a failure; the pores 



