DEVELOPMENT OF DISTICHOPORA VIOLACEA. 139 



oosperm nucleus fragments without any segmentation occur- 

 ring, giving rise to a simple multinucleated plasmodium. 



The eggs of Aphis (Will, 62) and some other insects contain 

 very little yolk, and do not segment until a large number of 

 nuclei are formed. 



The segmentation of the ovum, then, and the subsequent 

 formation of a morula mass of cells, are phenomena not 

 entirely dependent upon the absence of yolk. Many, compara- 

 tively speaking, large eggs, such as that of Rana, segment, 

 whilst others, such as that of Alcyonium, do not. 



We cannot, consequently, assert that when an ovum segments 

 it is simply repeating an ancestral phase, and that when it does 

 not segment it is prevented from doing so by the physical 

 obstruction of the yolk. 



The reverse of this is more probably true. The recent 

 brilliant researches of Driesch (9) prove that the segmentation 

 of the ovum is due to physical or mechanical laws, and we 

 cannot or should not derive any phylogenetic conclusion from 

 the phenomena of segmentation. 



We may even go further than this, and say that the develop- 

 ing ovum would not segment, but would naturally pass 

 through the stage of a multinucleated plasmodium, were it not 

 for the action of certain purely mechanical forces, with which 

 we are not at present fully acquainted. When these forces 

 cannot act upon the egg, or are in some way counteracted, the 

 ovum does not segment, whether it is laden with yolk 

 (Stylasteridse, many Insects, Elasmobranchs, &c.) or not 

 (Millepora). 



III. — On the Fragmentation of the Oosperm Nucleus. 



It is the belief of many eminent histologists that any process 

 of division of the nucleus other than that by karyokinesis or 

 mitotis is a sign of the degeneration of the nucleus, and the 

 approaching end of the life of the cells. 



Flemming says, " Fragmentation of the nucleus, with and 

 without subsequent division of the cell, is universally a 



