DEVELOPMENT OF THE GENERATIVE ORGANS. 715 



believed that he observed this phenomenon in the eggs of Chir- 

 onomus, but the appearances which he described are entirely 

 dissimilar to those which have been repeatedly observed in 

 Echinoderms and Worms ; it is probable that the changes he 

 saw were due to the contraction of the yelk, as he described 

 the outgrowth of amreboid processes which subsequently be- 

 came separated from the yelk. Whatever the explanation it 

 is indubitable that Robin saw nothing like the separation of 

 true polar bodies or directive corpuscles. He evidently re- 

 garded Weismann's polar globules as true directive cor- 

 puscles. His observations were made on the entire eggs. 



Amreboid contractions of the peripheral layer of the yelk 

 were observed by Brandt in Donacia, and it is possible that 

 Robin saw similar contractions in the eggs of Chironomus. 



The attention of many observers has recently been directed 

 to the nuclear changes which occur in the so-called germinal 

 vesicles of Insects' eggs. Heider, Henking, Korschelt, Rath, 

 Wheeler and others have written in considerable detail on 

 these changes, Henking's work appears to me the most ex- 

 haustive, and his observations may be divided into two sets, 

 (i) The changes which occur before impregnation, and (2) 

 those which occur in the eggs immediately after their deposi- 

 tion ; whether the eggs have been impregnated or not. 



The first set, dealing with eggs which have not been passed 

 through the oviduct, consist of minute observations on the 

 number and position of the fragments of chromatin contained 

 in the so-called germinal vesicle, or the nucleus of the lowest 

 egg-cell. These observations, judging by the figures given, 

 appear to me to be highly unsatisfactory ; and it is incompre- 

 hensible to me that, admitting the correctness of the observa- 

 tions, any conclusions whatever can be arrived at from such 

 variable appearances ; a few irregular granules, sometimes in 

 chains, at other times isolated and scattered apparently without 

 order in the interior of the nucleus, have been marshalled into 

 the most definite order, and the author sees in them indications 

 of the most definite changes. 



The second set of observations deal with eggs which have 



