218 BULLETIN OF THE 



In no case have I found any evidence of the existence of this body 

 before the formation of the second polar globule. However, there is 

 always to be found in hardened eggs, as soon as the female pronucleus 

 has become well marked, another structure resembling the female pro- 

 nucleus (Figs. 58, 60), which is usually located at some distance from 

 the animal pole. 



It ordinarily has almost exactly the same size as the female pronu- 

 cleus, and deports itself quite the same as the latter, when treated with 

 different reagents. From its position it is unquestionably the deeper 

 clear spot discovered in the living eggs. In the earliest condition in 

 which it has been satisfactorily observed, it has, with a single exception 

 (Fig. 70^), already attained a considerable size, and contains a number of 

 highly refractive spheroidal bodies. It is found at this stage (Fig. 60) 

 still not far removed from the surface of the vitellus. It becomes visible 

 in the living egg only at a later period, when it has altered its position 

 and attained greater dimensions. 



From its subsequent changes and ultimate fate there need be no 

 hesitancy in calling it at once the male pronucleus (mpn), even though 

 its relationship with a spermatozoon could hardly have been surmised, 

 but for the very conclusive observations made by several observers 

 within the past few years, — one might almost say months. In a 

 few cases toward the close of the constricting phenomena, which set 

 at liberty the second polar globule, and before a distinct female pro- 

 nucleus had appeared, I have noticed, very close to the surface of the 

 vitellus in the vegetative hemisphere, small vacuoles (diam. 6 jx) of 

 homogeneous appearance (Fig. 66), which I am inclined to consider as 

 earlier stages in the existence of the male pronucleus. The prepara- 

 tions were all such as had been produced by the use of acetic acid and 

 subsequent staining in Beale's carmine, which, as before stated, is less 

 favorable for making conspicuous the pronuclei than is the osmic acid 

 process. The interference of the granular elements of the yolk is such 

 as to make the observations on these small structures exceedingly diffi- 

 cult and little reliable, for which reason it may be better to consider the 

 object seen as only possibly bearing the interpretation suggested. The 

 doubt as to the significance of these structures was further increased 

 by the fact that in one case — the one figured — two such vacuoles 

 of almost identical appearance occurred in remote parts of the same 

 vegetative hemisphere. It might not be absolutely impossible, it is 

 true, that these vacuoles resulted each from the presence of a sperma- 

 tozoon, but it would be highly improbable, in the light of all that has 



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