OF AN EGG. 33 



instance that of Laomedea, (fig. 14,) a kind of 



Hydra. Finally, we come to the lowest degree, 



in which, as I have already described, the egg 



(figs. 10, 11) is a mere cell with a light spot in 



one part of the yolk. The eggs of Amosba are 



also in the same condition as the last. In this pi?. 14. 



case the parent of the egg is as simple in structure as the egg 



itself. 



What, then, are the characteristics of an egg? If the sharply 

 defined, concentric vesicles of the most complicated eggs are 

 not to be found everywhere, but on the contrary we see all 

 grades of definiteness and number as regards these apparently 

 special bodies, we must come to the conclusion that each vesicle 

 is not restricted within its own boundaries, even though its out- 

 line may have the appearance of a wall which would seem to 

 be intended to shut off direct communication with the outside. 



I think that the most straightforward solution of this problem 

 is, that the germinal vesicle, which is always present in some 

 form, either sharply defined, or, as I have shown, as a mere 

 transparent spot at one side of the egg, is simply an expression 

 of the concentration of albuminous matter at one pole; whilst at 

 the opposite, or, as one might call it, the negative pole, we have 

 the mass of yolk. 



That this is so, is demonstrated by the process of develop- 

 ment of the egg from its inception to its completion ; and as the 

 egg is a cell, and the type of all cells, its mode of genesis is 

 typical of all free-cell development. This I will illustrate by a 

 series of ideal figures (figs. 15, 16, 17, 18) of the progressive 

 stages of development of the theoretical egg; such a one as 

 would, in the progress of growth, pass through all the conditions 

 in which the egg has been known to exist in various animals. 

 As I have already said, the egg in its inception is a minute 

 aggregation of fluid matter; but this drop of fluid has not a 

 homogeneous, uniform density throughout; on the contrary, it 



Fig. 14. Egg of Laomedea amphora. Ag. 125diam. The Purkinjean vesicle 

 is filled with transparent, coarse granules. Original. 



3 



