DEVELOPMENT OF CTPRINODONTS. 907 



li«8 is broaght into direct commanication with the general ovarian space, which, sin- 

 gnlarly enough appears to be ocolnded from without by a temporary closure or plug- 

 ging up of the oviduct or canal from the posterior end of the ovarian eao, a snate of 

 affairs, which, if it can be confirmed, approximates, or, to some extent, resembles, the 

 condition found to obtain in a pregnant mammal, where the uterine os or mouth is tem- 

 porarily occluded during gestation. 



"We found onrselves unable to determine the species of the form, the structure of 

 which is described above ; none of those desciibed in Jordan's Manual appear to agree 

 with our species (Gambusw, patruelis, B. & G, — D. 3. J.). It may be, as some of us have 

 surmised, that the isolation of the form on the eastern peninsula of Virginia for a great 

 length of time may have served to develop specido characters, and that it is undescribed. 

 We leave the determination of the species to the systematic ichthyologists. 



" Thus far our account has dealt only with the structure of the adults and the peon- 

 liar contrivances by means of which reproduction is effected ; we will now take up the 

 discussion of the egg and embryo. 



"The globular vitellns measures about a line in diameter including the embryonic or 

 germinal portion. The germinal protoplasm probably occupies a peripheral position 

 covering the nutritive or vitelline portion of the egg as a continuous envelope with 

 strands of germinal matter rnnning from it through and among the corpuscles of the 

 vitellns. This peripheral germinal layer, when the egg is ready to be fertilized, mi- 

 grates toward one pole and assumes a biscuit shape, This is essentially the history of 

 the formation of the germinal disk of the Teleostean egg as worked out independently by 

 Professor Kupffer and the writer. Little of a trustworthy character is known of the 

 history of the germative vesicle and spot, which bear the same relation to the egg as 

 the nucleus and nucleolus do to the substance of the cell of the ordinary type. When 

 cleavage of the germinal disk has begun, it is the first positive evidence that impregnation 

 has been successful. The disk then begins to spread over the vitellns or jelk and soon 

 acquires the form of a watch glass with its concave side lying next the surface of the 

 yelk. Coincident with the lateral expansion of the germinal disk, a thickening appears 

 at one point in its margin which is the first sign of the appearance of the embryo fish. 

 With its still further expansion, the embryo is developed more from the margin of the 

 disk toward its centre ; in this way it happens that the axis of the embryo lies in one of 

 the radii of the disk; its head toward the centre, its tail at the margin. 



" But before the embryo is fairly formed, a space appears under the disk limited by 

 the thickened rim of the latter, and the euibryo at one side. This space, the segmenta- 

 tion cavity, is filled with fiaid and grows with the growth of the germinal disk, as the latter 

 ieeomes converted into the hlastoderm, and does not disappear until sometime after the embryo 

 has left the egg as a young fish ; and then it often remains as a space around the yelk sac 

 for as long as a vestige of the latter remains, as may be seen in the young of Cybium, 

 Parephippus, Gadus, Elecate, and Syngnalhus. In regard to this point, I hold views en- 

 tirely different from any other observers, but inasmuch as the writer has had opportu- 

 nities for the study of the development of a greater number of species representing a 

 greater number of families than any previous investigator, and because the observa- 

 tions are based on material studied without the use of hardening re-agents which either 

 deform or obliterate the segmentation cavity, and also because it was found to be present 

 in all of the forms which were sufficiently well studied, it is belicYed that it will be found 

 in the developing ova of most or all Teleostean fishes. Should this prove to be the fact, the 

 Teleostean egg will be as distinctly defined in respect to the sum of the developmental char- 



