REVERSIBILITY OF MORPHOGENESIS 11 



and larger member (figs. 21 b, 23 a, and 26). In those cases 

 where the members of the heteromorph were equal in size and 

 degree of differentiation there seemed to be a balance, and if 

 both of the individuals could take food and grow, the process 

 led to the separation into two potentially equal individuals; for 

 example figure 25. Other similar instances supporting these 

 conclusions were observed but were not drawn. It is clear that 

 in cases where there is inequality the larger piece has a tendency 

 to exhibit a control or dominance over the smaller one, but as 

 to its cause these observations tell us nothing (Child, '15, page 

 199). It is a peculiar fact that among all the heteromorphic 

 individuals observed not a single one had the anterior ends 

 pointing toward each other; that is to say no 'heteromorphic 

 tails' appeared. 



Another curious case illustrating how dedifferentiation may 

 proceed when initiated by conditions slightly different from 

 those described above, is the following. Figures 33 to 38 inclu- 

 sive « are freehand drawings made as carefully as possible of six 

 different conditions of an originally normal individual picked 

 out from a culture which had been fed with grains of boiled yolk 

 of hen's egg. When first observed (fig. 33), it was in the act of 

 division but .a string of yolk grains surrounded by a bridge of 

 protoplasm prevented separation of the sister cells. This bridge 

 of protoplasm remained as a connection between the individuals. 

 Figure 34 shows the two individuals six and one-half hours later. 

 Differentiation has proceeded normally in spite of the proto- 

 plasmic connection. After twelve hours the protoplasmic bridge 

 widened and parts of the endoplasm of individual B were seen 

 to flow into A by way of the connecting bridge of protoplasm. 

 Individual A gradually became larger while B became smaller. 

 This process continued until at twenty-nine hours after isola- 

 tion B had passed entirely into A as shown by the fact that two 

 distinct sets of quite fully differentiated active membranelles 

 were present, and A had now become much larger (fig, 35). 

 Increase in size was partly due to assimilation of the ingested 

 yolk grains, For about ten hours between the stages shown in 

 figures 34 and 35 the organism was not under observation, so 



