318 



cells of Batrachoceps, but the cutting-off and isolation of cytoplasmic 

 processes is never seen in Amblystoma, and consequently the blood 

 of this animal contains no structures corresponding to the blood 

 platelets of mammals. However, from what we know of the function 

 of spindle cells, and from Wright's description of conditions in Ba- 

 trachoceps, it seems that his conclusion, that the spindle cells corre- 

 spond to circulating megakaryocytes, is justified. Therefore, with 

 the single exception of Batrachoceps, the circulating megakaryocyte 

 (spindle cell) of Amphibia assumes the functions which, in mammals 

 are delegated to isolated parts of the megakaryocyte protoplasm. 



Werzberg has again opened up the question of the structure 

 of the spindle cell nucleus. He states that the chromatin is generally 

 arranged in the form of longitudinal bands which are separated from 

 each other by „Parachromatin". He believes that the longitudinal 

 light streaks (see fig. 6 of this paper) which are seen in the nucleus 

 are due to the presence of this "parachromatin", and not to folds on 

 the surface of the nucleus. As Werzberg has given a very compre- 

 hensive review of the literature of this subject no further discussion 

 of it is necessary here. 



The spindle cells of Amblystoma are very favorable material for 

 the study of nuclear structures. Here, perhaps better than in most 

 x\mphibia, we see that the light streaks are simply due to the presence 

 of grooves on the surface of the nucleus. Sometimes the grooves are 

 so deep that they give the nucleus a lobulated structure (smaller 

 end of the nucleus in fig. 6).^) Focusing on the light streak of the 

 nucleus shown in figure 6 shows clearly that this is the bottom of a 

 very deep groove. The groove appears light because the nucleus is 

 thinner here than elsewhere, and consequently more light is trans- 

 mitted through the region of the groove than through any other part 

 of the nucleus. The right-hand end of this nucleus shows such a groove 

 in optical section. The nuclear membrane is invaginated, and the 

 groove is filled with the hyalin intergranular protoplasm of the cell. 

 If this appearance were due to the presence of "Parachromatin" the 

 nuclear membrane would be rounded evenly over the end of the 

 nucleus, and it would be impossible to trace the protoplasm into the 

 nucleus. Such grooves are seen on the surface of nearly every 



1) According to Jordan and Flippin the nucleus of the spindle cells of 

 Chelonia " seems split into several parts or cut through hy one or several 

 furrows." 



