2l6 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



cells function as mesenchyme or remain as inhibited cells is not known, 

 except for the fact that some of them may form epithelial vesicles in 

 echinoids (pp. 238-39). 



SECONDARY AND COELOMIC MODIFICATIONS 



Forms resulting from temporary exposure in early stages to severe in- 

 hibiting conditions, but with slight secondary modifications, are shown 

 in Figure 86. In A the only indication of possible differential recovery is 



Fig. 87, A-E. — Differential recovery in water after differential inhibition. A, B, Patiria, 

 LiCl m/20, 10^ hr. from early blastula; C-E, Asterias; C, D, KCN m/200,000, continuous from 

 one-cell stage but with gradually decreasing concentration after 2 days; E, Patiria, LiCl m/30, 

 21 hr. from two-cell stage. 



the elongation, the earlier gastrula being flattened apically; B shows sim- 

 ilar elongation and an apical mouth; slight apical thickening and out- 

 growth appear in C, but there is complete breakdown of entoderm, except 

 a thin outer layer; apical recovery is evident in D. With somewhat less 

 extreme inhibition further development and more or less differential re- 

 covery follow return to water, but ventrodorsality may be completely or 

 almost completely obliterated. In Figure 87, A and B, lithium forms of 

 Patiria, have apparently completely radial ectoderms, but the form of 

 the enteron in A suggests that some slight ventrodorsality is still pres- 

 ent or was present at a stage affecting entodermal development. In B 

 there is no evidence of ventrodorsahty ; and C, D, and E, modifica- 



