464 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [10"j 



ill this manner. This structure has been called the nuclear net work or 

 reticulum. Such reticuli have been observed in the gerraiuativ^e vesi- 

 cles of the eggs of Hydra, stnr- fishes, sea-urchins, a,nd fresh-water mus- 

 sels; by the writer in the eggs of the clam, 03'ster, common slipper 

 limpet, and gar-pike; by Van Beneden in the ovarian eggs of batsf 

 by Balfour in the ovarian eggs of sharks; by Rauber in the ova of osse- 

 ous fishes; so that their occurrence is probably almost universal through- 

 out the animal kingdom. Not only are egg-cells found to have such 

 reticuli developed in their nuclei, but they are also found developed in 

 white blood corpuscles and many other kinds of histological elements. 

 The extraordinary similarity in the character of many of these reticuli 

 is very striking, and argues for the existence of a similar cause in their 

 production in the diverse forms in which they occur. In Flemming's 

 elaborate researches nuclear forms of such complexity have been de- 

 scribed as to put one's credulity to the test, but more recent investiga- 

 tions of my own with his methods have convinced me that such struct- 

 ures do exist, and that we have hitherto missed them only for want of 

 the means of demonstration. 



The fate of the germinative vesicle when the egg has reached matur- 

 ity is still involved in some obscurity as far as concerns the eggs of 

 fisheis. That it disappears before the egg leaves the follicle in which it 

 was developed there can be but little doubt, for as soon as the ripe 

 eggs have fallen into the intraovarian cavity they are found to have 

 lost all trace of the conspicuous germinative vesicle or nucleus which 

 was so characteristic of them in their immature condition, and to have 

 acquired a transparency and homogeneity in which no trace of a nu- 

 clear body can be made out with the most cautious use of reagents. In 

 this, Hoffmann has been more fortunate than myself. This is conspicu- 

 ously the character of the ripe egg of the cod. When first removed 

 from the ovary, the vitelline membrane is somewhat lax, but as soon as 

 it is placed in water it slowly absorbs it through the micropyle, and 

 soon becomes tense from an imbibition of that fluid, which occupies a 

 sijace all around the vitellus between it and the vitelline membrane. 

 Impregnation seems to be necessary in some species before any water 

 can be absorbed; this is especially the case with the ova of the shad, 

 but is in a lesser degree necessary in the case of the cod. Practically, 

 these facts are of great use, as in the instance of the shad, where the egg 

 acquires several times its original dimensions, and when impregnated and 

 "water-swollen" it is said that the eggs have "risen," which may be 

 taken as a very sure indication of the fact that impregnation has taken 

 place. The same eggs unimpregnated will not become " water-swollen" 

 until a much longer time has elapsed, a very large proportion of them 

 not at all, which shows the remarkable influence exerted by the en- 

 trance of the spermatozoa through the micropyle upon the power of the 

 egg membrane to absorb water. It would appear as if the sperma- 

 tozoon, in making its entry, had oi^ened a passage-way for the water. 



