DEVELOPMENT OF DISTICHOPOEA VIOLAGEA. 6[ 



nuclei make their appearance in greater or less numbers ac- 

 cording to the more or less advanced stage of the blastema." 

 It is extremely improbable, if the minute nuclei in the 

 blastema could be observed by the simple method of treat- 

 ment with acetic acid, that the karyokinetic divisions of the 

 large oosperm nucleus, if they really occur, would have been 

 overlooked. 



Many other instances could be given from the writings of 

 naturalists during the last twenty years of the failure to trace 

 the divisions of the oosperm nucleus in insect eggs,, and of the 

 occurrence of "free nuclear formation" in the eggs after 

 fertilisation ; but in many of these instances it might be urged 

 that sufficient patience was not exercised, or that the methods 

 of preservation and staining were imperfect. 



An important paper has, however, been recently published 

 by Henking (23) containing an extremely elaborate account 

 of his investigations upon many different species of insects 

 carried on with the aid of the best modern methods of re- 

 search. It would take me far beyond the limits of this paper 

 to give even an outline sketch of Henking's important results, 

 but a brief reference to some of the points bearing upon the 

 subject of this essay must be made. 



In Pyrrochoris, one of the Hemiptera, Henking finds that 

 in the formation of the polar bodies the nucleus divides by a 

 process of karyokinesis, the chromatin bodies being of con- 

 siderable size and definite in number. 



After fertilisation a new spindle is formed with the chromo- 

 somes arranged in an equatorial plate, but before the division 

 is completed the chromosomes disappear. Later on the 

 chromosomes reappear in the form of extremely minute and 

 numerous granules, which fuse together into threads, and 

 arrange themselves in the equatorial plate of a new spindle. 



Similarly, in Agelastica alni, a Coleopteran, the chroma- 

 tin entirely disappears after the division of the segmentation 

 nucleus. 



In the Hymenopteran Lasius the chromatin of the first 

 two segmentation nuclei completely disappears, and when the 



TOIi. VI. 6 



