214 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



lar stages may entodermize prospective ectoderm, but later it inhibits 

 and dissociates entoderm; the increase in entodermal susceptibility ap- 

 parently occurs at a somewhat later stage in asteroids than in echinoids, 

 as does the increase in rate of dye reduction (pp. 134-37)- Inhibition be- 

 ginning in early stages may prevent gastrulation, but with long-continued 

 exposure dissociation into the blastocoel of entodermal cells may take 

 place without invagination; apparently, increase of entodermal suscepti- 

 bility is possible without invagination. 



Fig. 85, .4-F.— Loss of epithelial character and dissociation of the entodermal region in 

 Patiria with relatively extreme differential inhibition continuing to gastrulation or later. 



Different degrees of entodermal dissociation with more extreme inhibi- 

 tions are shown in Figure 85, C~F; in C there is some invagination, and 

 dissociation is beginning apically; in D invagination apparently began, 

 but the whole prospective entoderm, except for a thin external layer, has 

 lost its coherence; in E and F gastrulation is completely inhibited, and the 

 cell immigration from the entodermal region resembles immigration of 

 mesenchyme in echinoids; there is apparently some entodermization in 

 E and in F. In Figure 85, A and B are effects of LiCl, C is from a lot in 

 KCN, D from sea water at pH 7, £ from another lot in KCN, and F from 



