180 THE AMERICAN MONTHLY [October, 



formed. This envelope is the follicle from one of the cells of which the egg 

 was originally formed, and by the cells of which it has been nourished and 

 built up. Very pretty pictures of the very regular follicle epithelium can be 

 formed by killing the egg with its follicle in alcohol instead of in acetic acid, 

 as before, and then treating the preparation on the slide with h^ematoxylin 

 or one of the carmine stains. These could be permanently preserved in 

 glycerine jelly, or, after proper treatment, in balsam. They help out the 

 observation of the section in regard to the structure of the follicle epithelium. 

 The egg within is so opaque that but little can be seen of its structure in this 

 way, and we must rely upon sections for additional information respecting it. 

 If we crush one of these eggs we can see that the yellow yolk is made up of 

 numerous small droplets, and that the spot in the centre is a clear body with 

 an extremely fine line limiting it. The spot in the centre is the gei-ininal 

 vesicle or nucleus, and the egg is really a cell, though one very unlike the 

 cells we have met thus far. 



2. The youfiff eggs. — The smaller bodies found in the angles between the 

 large eggs, and named the young eggs, are at first sight very unlike the eggs. 

 They are not only smaller in size, but very variable, most being perfectly 

 transparent while still alive, but some of the largest are yellowish and 

 opaque. Young eggs are the source of the eggs just described, and they 

 grow from extremely minute bodies hardly at all egg-like. The young egg., 

 unlike the mature one, is of all varieties of shape, for it seems to be obliged 

 to take on any shape the space between the large eggs permits. It is not 

 often round, but usually oval or flattened. Each one is seen to have a thin 

 follicle around it, the pavement epithelium of which can be demonstrated, 

 but not quite so clearlv as in older eggs, because the egg fills the follicle more 

 compactly. The egg itself consists of a translucent, faintly granular body 

 and a central, very clear nucleus or vesicle. The body is colorless and gives 

 no evidence of the presence within it of the yolk substance. It is composed 

 of nearly unmodified protoplasm, and the youngest eggs are hardly different 

 from the kinds of cells already met, except in shape and mode of attachment. 

 The nucleus is large, has a very sharp, thin line bounding it, and is very 

 transparent in a perfectly fresh egg. The nucleus contains, besides the trans- 

 parent substance, a number of minute droplets which always lie close to its 

 margin. In an egg which has stood long enough for the protoplasm of the 

 nucleus to die, the nucleus is found to be not empty, but to contain matter, 

 then seen as granular, which is scattered through it in such a way as to leave 

 many clear spaces. The epithelium of the follicles becomes much clearer in 

 the dead eggs. It is possible to bring out these facts by killing the cells with 

 alcohol by irrigation, when the protoplasm coagulates and becomes visible. 



Besides the eggs Vv'ith their coverings, the latter being in truth the ovary, 

 while the former are but its products, there is still the whitish substance 

 which, as 3'ou remove the eggs, you will see forming a sort of ground sub- 

 stance in which the eggs are held. If you wish to examine it further you 

 should first cover a bit of it for a moment with alcohol, then for a few min- 

 utes more w^ith borax-carmine, then wash this out with acidulated alcohol. 

 Then cover the specimen and examine it in alcohol. All this can be done 

 in a few minutes, by treating the specimen on a slide from the start. It will 

 demonstrate the cellular character of this whitish substance. Many long nar- 

 row cells are found, possibly muscular, but more careful treatment would be 

 required to determine more than that the substance was an important tissue 

 of the ovary. 



IV. General conclusions. — Having examined both preserved and fresh 

 preparations of the ovary of the cray-fish, we are now in a position to form 

 some conclusions upon the organ and its physiology or mode of action. 



