414 BULLETIN OF THE 



presents a radiated appearance, which the author does not, however, fur- 

 ther describe. These latter stages are exhibited by unsegmented eggs 

 found in company with eggs ah*eady divided into two segments, taken 

 from the middle or from the lower half of the oviduct. 



From all this it is concluded that the first embryonic nucleus is devel- 

 oped at the expense of two pronuclei, one peripheral, the other central. 

 As the spermatozoa have already been shown to become mingled with 

 the superficial layer of the yolk, it is probable that the peripheral nu- 

 cleus is formed, at least partially, at the expense of the spermatic sub- 

 stance. " If, as I think, the central pronucleus is formed exclusively 

 from elements furnished by the egg, the first nucleus of the embryo will 

 be the result of the union of male and female elements." This latter, 

 however, he expressly states, is only an hypothesis. 



In the description of the polar globules there is a notable deficiency. 

 Although a fundamental difference is maintained for the two globules, 

 we are not informed of the order in which they make their appearance. 

 In the present state of our knowledge it can hardly be granted that there 

 is any such fundamental distinction between the two as Van Beneden 

 maintains ; it would nevertheless be interesting, and possibly not with- 

 out important significance, to know if in any case there is a noticeable 

 difference in the intensity with which these globules respond to the in- 

 fluence of reagents, especially of staining fluids. For Limax I can only 

 report, without having directed particular attention to the point during 

 my observations, that I have not noticed any constant difl^erence, though 

 I should not wish to assert positively that a more careful study, limited 

 to this single point, would not teach otherwise.* 



In another direction the studies of Van Beneden are of especial inter- 

 est. I refer to the condition of the two pronuclei, which he has described 

 as a moulding of the central (female) upon the peripheral pronucleus. 

 The possibility of this condition having been produced by the influence 

 of the hardening reagent (osmic acid), does not seem to have occurred 

 to the author. The more I reflect upon it, the more it seems to me this 

 condition may be attributable to the same cause as that which produces 

 similar conditions already described for eggs of Limax treated with the 



* There are, however, some reasons why it would be difficult to reach entirely con- 

 vincing evidence on this point. A comparison between the first globule of one egg 

 and the second of another would have to deal with unknown individual differences in 

 the eggs, and other possible diff"erences of conditions ; while in a comparison between 

 the two globules of the same e^g one could not ignore the possibility of changes (of 

 degeneration) in the older of the two globules which would seriously diminish the 

 value of such comparisons. 



