ROBERT CHAMBERS 



57 



Fig. 4 a to d illustrates a similar case in which the non-nucleated 

 masses are considerably larger than those depicted in Fig. 3. The 

 similar behavior of one of the first two blastomeres in an egg is shown 

 in Fig. 5 a and b. 



In the remaining three cases the astral radiations faded out during 

 the operation (Fig. 6 a). The original segmentation furrow gradually- 

 filled up and disappeared (Fig. 6 b) and each piece assumed the ap- 

 pearance of a normal blastomere. The nucleus then shifted so as to 

 occupy a more central position in what one may term the reconstructed 

 blastomere and further segmentation proceeded as if the ovum had 

 not been operated upon (Fig. 6 c and d). This procedure always 



Fig. 5. Effect of a diagonal cut through one of the first two blastomeres of an 

 Asterias ovum, a, egg showing direction of cut. b, cut blastomere a few minutes 

 later. 



occurred when the ovum was consciously rolled during the opera- 

 tion so as to produce a disturbance evidenced by a churning move- 

 ment of the egg constituents. 



A similar instance in the case of an Arbacia egg is shown in Fig. 

 1 a to c. A piece was cut from one pole of the amphiaster egg. In 

 the process the piece was cytolyzed. The amphiaster in the remain- 

 der of the egg disappeared to reappear again in a new position with 

 the result that two equal sized blastomeres were formed. 



That mechanical disturbances may cause a reversal of a solid to 

 a fluid state has already been shown.^ This would make all the 



