142 THE AMEEICAN MONTHLY [August, 



ure, and perhaps the novice might at first suppose it a body composed of 

 numerous cells. We shall leave that point for the present to return to it later 

 on, and study first the various parts seen in the egg. It is bounded by a sharp 

 fine line w^hich shows no structure, it is a thin membrane which entirely en- 

 velopes the egg after the manner of a cell wall investing the ordinary cell. 

 It is known as the vitelline membrane, from the term vitellus, the name for 

 yolk, and is the coat which encloses the yolk and the egg. The vitelline 

 membrane does not in section form a complete circle as it would of necessity 

 were the egg a perfect sphere, but is polygonal in outline. The eggs, as could 

 be shown by studying a series of sections, are flattened against each other, 

 thereby proving the flexible character of the vitelline membrane. Within the 

 vitelline membrane may be seen a fine granular substance_^, which stains readily 

 and pervades the entire egg ; this forms a sort of ground substance in which 

 the larger granules are deposited. The finely-granular, deeply-staining matter 

 of the egg is protoplasm. It has the same appearance to the eye, whether 

 fresh or in sections, and stained or unstained, as the protoplasm in cells of the 

 green gland or ' liver.' Scattered through the protoplasm everywhere, except 

 in the centre of the eggs, may be seen small oval bodies y of various size. 

 These are globular masses held in the protoplasm. In sections they stain or, 

 better, tint evenly, but not deeply ; they are homogeneous, often hyaline, 

 but in some cases not quite hyaline, but more like very fine gi"ains of 

 ground glass. These grains are the usual constituent of the yolk of those 

 eggs which have a yolk. They form the bulk of the egg of the cray-fish, and 

 give it its yellowish brown color. The substance of which the grains are 

 formed is believed to be albuminous because of its reactions, for it does 

 not dissolve in turpentine nor turn blue with iodine. It is a substance 

 made by the active protoplasm, and stored as food to be ready for use 

 when the egg begins to develop. Since the egg is comparatively large, and 

 the germinal vesicle /i occupies only a small part of it, anyone can readily 

 see that several sections passing through the middle of the egg on both sides 

 will fail to intersect the vesicle. There will on that account be a num- 

 ber of eggs cut in each section which will show in their centre only proto- 

 plasm. In some, however, a central body may be seen, plain, unlike the 

 protoplasm, and separated from it by a sharp, thin line. The central body 

 is the germinal vesicle, is more open than the general protoplasm outside it, 

 which gives it a lighter color, but the coloring matter may be seen to take a 

 stronger hold upon the colorable substance in the vesicle than is the case in 

 the egg at large. The outline of the vesicle wall is not perfectly circular, as 

 shown in fig. 4, but this may be due to the action of the hardening reagent, 

 for, as we shall see, the vesicle usually looks spherical in eggs examined in 

 the living condition. Examination of the vesicle will show that near its 

 periphery larger and more deeply-stained spots are seen forming a sort of zone 

 of substance not unlike the general substance of the vesicle in composition, but 

 greater in bulk. Without here reviewing the present known facts in the 

 case, I may merely say that the biological writers are by no means agreed 

 upon the structure of the vesicle, or the meaning of the light and dark, but 

 they are agreed in finding here two substances, one of which stains and the 

 other of which does not stain. The deeper tinted larger spots in the periph- 

 eral zone are the bodies known as nucleoli, which are only larger masses of 

 the stainable substance. 



After this review of the parts found in the egg, it would be expected that I 

 should next try to discover the part played by each, if that be possible ; this 

 question I will adjourn till the_close of the present chapter. I wish, however, 

 to delay at this point long enough to suggest the answer to the question 

 asked a moment since, viz : — What is the cellular status, so to speak, of the 



