4G2 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [8 J 



after a cousiderable time, several days or even two weeks after hatching, 

 according to the species. 



The mucus usually found in the functionally active ovary, completely 

 covering the ova which have fallen into the ovarian cavity, is of consid- 

 erable interest. Its origin is somewhat obscure, but it is in the highest 

 degree probable that it is derived from the follicles at the time of their 

 rupture and the escape of the eggs. It is evidently a lubricant to facil- 

 itate the escape of the ova from the ovarian cavity or abdomen into the 

 open water. In other cases, where the ova are enveloped in an adhesive 

 mucous material, as in the cases of Perca, Cottus, Idus, Esox, Clupea, 

 Pomolobus, Apeltes, etc., its function is altogether different, and serves, 

 in addition, either to glue the eggs together in masses or bands, or to 

 cause them to adhere firmly to fixed objects in the water. Sometimes 

 the eggs adhere in ribbon-like masses, such as is said to be the case with 

 the eggs of the perch {Perca flavescens). Mr. G. P. Dunbar reports in the 

 American Naturalist that the eggs oi Atractosteus are held suspended 

 in a thick, jelly-like substance, forming long ropes several inches in 

 diameter, which are hung on old snags, roots, or branches of trees that 

 have fallen into the water. The spawn has much the appearance of 

 that of the frog, with the exception of the form it assumes and the size 

 of the eggs. Other contrivances for the suspension of fish ova have 

 been described by Haeckel and Kolliker, and more recently more fully 

 investigated by myself in Tylosurus, Hemirhamplius, and Ghirosto7na, 

 consisting of a garniture of fine filaments which partially clothe the sur- 

 face of the membrane. These filaments are developed within the ova- 

 rian follicle as processes of the envelope of the egg, around which they 

 are closely coiled until brought into contact with water. The peculiar 

 mucus which hardens under water is probably also developed as a se- 

 cretion of the ovarian follicle in most cases ; in others there doubtless 

 exist glands which secrete this material, in the same mann-er as we find 

 a special secretory sack in the male of Apeltes, from which the material 

 for the fibers is derived with which the animal binds together the parts 

 lof its nest. 



As far as my own investigations enable me to judge, the history of 

 the process of the maturation of the ova of bony fishes in general is 

 very similar, but there are modifications of the process, the nature of 

 which can only be ascertained through a study of the growing ovaries 

 of representatives of the various families known to the ichthyologist. 

 It is probable that even this will not suffice, for the most unexpected 

 ])ecu]iarities are found to be very characteristic of the eggs of a species 

 closely related to some other. As an example of this, the egg of the 

 shad may be mentioned as differing very greatly from the egg of the 

 herring, in that the former has a very much more spacious breathing 

 chamber surrounding the vitellus or yelk than the latter. It is not ad- 

 hesive, a characteristic by which it may be again distinguished from 

 the egg of the herring. Such peculiarities are no doubt related to some 



