Germ Cells of Leptinotarsa Signaticollis. 177 



constant size and number are found, but no astral radiations 

 appear. 



Furthermore, it is to be noted that among the protozoa and 

 unicellular plants where mitosis may be said to exist in its most 

 primitive form, the nuclear membrane remains intact and does 

 not disappear at any stage of the division. This condition is 

 characteristic of amitosis while on the other hand rupture of the 

 nuclear membrane at some stage is an accompaniment of mitotic 

 division. Again, in the lower forms the arrangement of the chrom- 

 atin granules to form chromosomes appear to be of secondary 

 importance as compared with the higher forms and the essential 

 feature in nuclear division appears to be the fission of the indi- 

 vidual granules. 



These facts all point to the origin of mitosis from a primitive 

 amitotic method of divisions, and therefore give considerable 

 ground for a phylogenetic interpertation of amitosis. 



Owing to the usual association of amitosis with degeneration, 

 I at first thought that the degenerated area in the testis would 

 furnish an explanation of the direct division in the early sper- 

 matogonia. I soon found, however, that only epithelial cells 

 participate in the degeneration, and that so far as I was able to 

 determine, the spermatogonia undergoing amitosis later develop 

 into functional germ cells. 



What then is the significance of the degeneration? The phen- 

 omenon recalls certain peculiarities in the development of the 

 ovary. In the first place, it might be compared with the changes 

 following the accumulation of epithelial cells at the base of the 

 terminal chamber, which results in the effacement of the sharp 

 line of demarcation between the latter and the cells of the tube 

 stalk; but the appearance of the cells in the two cases is entirely 

 different. In the ovary, the nuclei of the cells involved undergo 

 a kind of liquefaction, whereas in the testis the cells disintegrate 

 into irregular fragments. 



Physiologically the process may be analogous to the change which 

 converts certain of the germ cells of the female into nurse cells. 

 The degenerated area of early stages is actually much larger than 

 later on when it is represented by the part enclosed in the cyst, 



