A STATISTICAL STUDY OF MITOSIS AND AMITOSIS. 243 



tissue, can however be supported by several references in the 

 literature, and these I shall at least mention. 



I have already referred to the work of Meves ('91) on the 

 spermatogenesis of the salamander. In this well-known paper 

 evidence is brought forward which shows that in the sperma- 

 togonia amitotic divisions take place during the fall, and that 

 these succeeded in the following spring by the usual maturation 

 phenomena, are part of the cycle of a normal organism. Wheeler 

 ('89), in his paper on the embryology of Blatta germanica and 

 Doryphora decemlineata has reached similar conclusions. Thus 

 in Blatta, cells originate in the center of the ovum by mitosis. 

 These cells are amoeboid, and wander to the surface of the egg 

 where they flatten out. " The cells which have reached the sur- 

 face and are much scattered over the roof-shaped ventral face and 

 the adjacent portions of the lateral faces commence dividing longi- 

 tudinally, not by karyokinesis, as heretofore, but by akinesis." 

 "My observations," continues Wheeler, "tend to show that all 

 of the future divisions in the formation of the blastoderm, and 

 those subsequently undergone by the serosa, are akinetic, the 

 densely coiled chromatin filament remaining inert and the 

 divisions taking place by a constriction which often produces two 

 daughter nuclei of very unequal size. I emphasize the fact that 

 these forms of division could not have been produced by the 

 reagents, as the eggs were hardened in picro-sulphuric acid or 

 simple alcohol, which in younger and older eggs preserve the 

 karyokinetic figures of the cleavage nucleus and its immediate 

 descendants with great clearness." From this it follows that the 

 cells that make up the germ-layers from which the definitive cells 

 of the body come, are all descended from cells which at an 

 earlier period of development divided by amitosis. 



Frenzel ('92) came to the conclusion that amitosis plays an 

 important role in the regeneration of the intestinal elements in 

 the crustaceans, and insects, for he claimed at first never to have 

 found any indirect divisions. As Henneguy ('96) pointed out 

 after Frenzel himself had corrected the mistake the conclusion 

 that mitosis does not occur in the cells in question is undoubtedly 

 incorrect, but the fact that the digestive tract in certain arthropods 

 can be studied carefully without revealing any mitotic divisions, 



