184 BULLETIN OF THE 



region of the animal pole, never losing wholly its unlikeness to the rest 

 of the yolk, after a time shows a faint light spot of more or less cir- 

 cular form. At first this spot is always poorly defined, and in many 

 cases remains thus as long as it continues to be visible. In other cases, 

 especially when it is nearer the animal pole, one may at length discover 

 a clear-cut delicate outline, which always remains concave toward the 

 centre of the spot. The latter is usually circular, but sometimes it is 

 oval, and sometimes it has the form of an irregular body with rounded 

 angles. This nuclear body continues gradually to increase in size, and 

 at the same time to undergo slow changes of form, which, however, have 

 never been seen to exceed the limits above indicated. When it has 

 reached the size of the smaller polar globule, or somewhat earlier, a 

 second like clear spot is seen lying deeper in the vitellus, and conse- 

 quently less clearly defined (Figs. 21, 36). These bodies at first appear 

 homogeneous, and less refractive than the surrounding protoplasm. 

 Very soon, however, a few (1 - 3) small highly refractive corpuscles (nu- 

 cleoli) may be seen in them at some distance from each other. They 

 change their relative positions only slightly, as though passively shifted 

 by the changes in the form of the nuclear body. The corpuscles in- 

 crease in number, but I have not observed a division in any of them. 

 The increase in the size of the nuclear bodies is quite gradual; they 

 may attain, however, (Fig. 65,) a very considerable diameter (35 /x). 

 They are respectively, the first, the so-called egg-nucleus, or female pro- 

 nucleus ; the second, the male pronucleus. 



The formation and growth of the female pronucleus, which occupies 

 from one to two hours, according to temperature, constitutes the last 

 series of changes which belong to this head, — the phenomena of matu- 

 ration, — and we may now direct our attention to the results obtained in 

 studying this phase of egg development by other means. 



For the purpose of pursuing the phenomena transpiring within the 

 yolk, — which for the most part can only be traced with difficulty, or not 

 at all, in the living specimen, — one may have recourse to treatment 

 with various reagents. Acetic acid has furnished the means to this end 

 in the greater part of my studies. 



The condition presented by the least advanced eggs which I have 

 been fortunate enough to secure was such as to contribute almost noth- 

 ing to the solution of the question, What is the exact relation between 

 the germinative vesicle and the first, or maturation, spindle ? The eggs 

 of Li max are not favorable objects for the study of this important ques- 

 tion, — which has of late been agitated with such a fair prospect of a 



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