458 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [4] 



erally abandouecl. CEllacber argues for its composite nature, as dovn 

 Kupffer in the case of the herriug's egg. Balbiaui thinks it best to adoj )t 

 the name of egg-capsule for the covering of the egg, as by that means 

 he does not commit himself as to its origin. 



The micropyle of the fish ovum was first observed in the egg of Si/it- 

 (jnathus opMdion, one of the pipe fishes, by Doyere, in 1849 ; the next ob 

 servations were those of Eansom and Bruch, 1855, and it was afterwards 

 more fully discussed by the former. 



The pore canals in thfe zona radiata were discovered by Johannes Miil- 

 ler in 1854. 



Sars has counted the laminae in the vitelline membrane of the cod's 

 egg, but the writer has not been able to assure himself so fully upon this 

 point. Under ordinary conditions, Avhen a portion of the membrane is 

 examined which has been sharply folded upon itself, no sucli laminar 

 structure is visible until subjected for some time to the action of a 1 per 

 cent, solution of osmic acid, when the laminated structure spoken of is 

 produced, but whether simply by the action of the acid or as a normal 

 feature of the structure of the membrane may be a question. 



The immature ovarian eggs of the cod may be studied by taking an 

 ovarian lobule from the ovary of an adult female and placing it in a 

 compressorium under the microscopf. Under a power of 150 diameters^ 

 we learn that, while there are many eggs one-half or fully grown, thei'e 

 are many more which are very immature, and are only revealed to our 

 vision by the aid of considerable magnification. Nor is this all; we find 

 that there may be three well-marked stages of egg development distin- 

 guished. These are best seen when the fragment of ovarian tissue has 

 been subjected to sufficient compression to render the ova more apparent 

 by transmitted light, and if the observer will take care to use a 1 per 

 cent, solution of acetic acid, the nuclei of the unripe eggs will be bronght 

 into bold relief by the action of this reagent in a few minutes. He will 

 notice, first of all, that the immature ova measure all the way from a 

 little over 1°'™ down to a very few hundredths. The smallest ova are 

 involved in the fine cellular material of the ovary from which the eggs 

 themselves are slowly differehtiated as the growth of the ovary proceeds^ 

 when well supplied with blood and nutritive matter, previous to and 

 during the spawning term. When once large enough to be readily 

 distinguished from the indifferent cells which inclose them, the growing- 

 egg, or ovicells, are distinguished from the mature ones by inclosing 

 inside them a comparatively large and very granular rounded body, 

 the nucleus or germinative vesicle, which frequently measures half as 

 much in diameter as the whole egg. The protoplasm which surrounds 

 the germinative vesicle is granular, quite transparent, and of a yellowish 

 Or pale amber tint, while the vesicle itself is darker in color and more 

 opaque on account of its granular walls. The position of the germina- 

 tive vesicle is always central in these immature eggs, and it is not until 

 the ova are approaching maturity that any marked change in its form 



