No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 323 



present ; from these differences in form he concludes that the 

 nucleolus may be capable of amoeboid movements. Subse- 

 quently it wanders towards the center of the nucleus, becomes 

 larger and more spherical. When the chromatin has assumed 

 the characteristic radial distribution, before the first maturation 

 division, the nucleolus passes again towards the periphery, and 

 there becomes gradually smaller, partly by fragmentation, and 

 so gradually disappears. 



Holl {'90) found one spherical nucleolus in ova of the newly 

 hatched chick : " Da das Kernkorperchen so auffallend verschie- 

 den vom Kernnetze und Kernsafte hinsichtlich des Verhaltens 

 zur Farbe sich zeigt, so muss es wohl aus einem anderen Stoffe 

 bestehen als jene. Auch bei Saiamandra, Rana, und Lacerta 

 fand ich das Kernkorperchen immer sich verschieden halten 

 von den anderen Theilen des Kernes." The nucleolus is always 

 situated excentrically at the upper pole of the nucleus. Towards 

 the end of the spirem stage the nucleolus lies on the periphery 

 of the chromatin, with which it stands in no close connection ; 

 it is no longer present in ova of 491 /a diameter. 



Kastschenko ('90) investigated the maturation of the ova of 

 Pristiurus, Scyllium, and Torpedo : there are numerous nucleoli, 

 which attain a diameter of i6/i, and all disappear at the 

 spirem stage (in the prophase of the first pole spindle). Each 

 nucleolus contains a large unstaining globule (but in his Fig. i, 

 in several of the nucleoli, all of which had been stained with 

 borax carmine, this globule is colored blue, while the peripheral 

 portion of the nucleoli is red). 



Masius ('9o) : in the ovum of Asplanclma the nucleolus forms 

 the greater part of the nucleus. In Lacinularia it is at first as 

 in the preceding genus, but at a later stage several much smaller 

 nucleoli are found. 



Mellissinos and Nicolaides ('90), pancreas cells of Canis : The 

 " Nebenkern " is a plasmosome which has wandered out of the 

 nucleus; this migration is caused by an injection of pilocarpin 

 into the living gland. 



Sheldon ('90) found one germinal spot in Peripahts capensis, 

 which disappears when the nucleus reaches the periphery of 

 the egg. 



