456 THEOPHILUS S. PAINTER 



variability which the monaster eggs show in their behavior. 

 These changes bear no direct time relation with the controls, 

 the movements appear early or late, and continue for a shorter 

 or longer time. (Direct evidence of this will be shown in the 

 sections). In spite of this variation, however, there is a sim- 

 ilarity in the behavior of all monaster eggs. 



First there is always a swelling of the ectoplasmic layer before 

 any sign of protoplasmic movement appears, and this swelling 

 does not begin until the chromosome vesicles are being formed. 



Second, the swelling invariably precedes the movement of 

 the protoplasm. 



Third, the severity of the protoplasmic movement seems to 

 depend on the distance which the aster retreats from the center 

 of the egg. When this retreat is extreme, we have a severe 

 movement, figures 1 to 5, when it is not marked, there is little 

 movement, figures Bi to B 6 and D x to D 6 . 



An additional feature of the behavior of the monaster eggs 

 should be emphasized. This relates to the ectoplasmic layer. 

 It not infrequently happens that the swelling of the membrane 

 is accompanied by the appearance of little granular irregularly 

 shaped bodies in the otherwise homogeneous layer. This almost 

 invariably happens in the two cell stage, as is shown in figures 

 B 5 and in Ai and A 2 . When the two cells move apart, after 

 the first division, this layer does not sink in as it does in the 

 normal eggs. But it remains in the condition shown in the 

 last figures named. Very frequently this swelling leads to the 

 disintegration of the layer so that in the later stages, it is not 

 present. As a result the blastomeres may become more or 

 less scattered, as shown in figure B 6 , but this does not seem to 

 interfere with the formation of blastulae or gastrulae. 



Internal changes 



In taking up the study of sectioned material of monaster 

 eggs, two main points were to be determined, first, the cause for 

 the divergence in the later behavior of the eggs, and, second, 

 the exact condition of the aster and chromosomes just prior to 



