2l8 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



and foregut are usually relatively large ; and the ventral surface is almost 

 or quite flat, rather than concave. All degrees of this modification occur 



Fig. 88, A~I. — Secondary modifications of Patiria following differential inhibition. A-D. 

 forms with slight apical recovery resembling echinoid preplutei in form, developing in water 

 after LiCl m/20, m/25, m/30, 10-21 hr. from early cleavage; £, differential recovery after 

 21 hr. LiCl m/30 from two-cell stage; F, differential recovery after 145 hr. LiCl m/30 from 

 si.xty-four cell stage; G, differential recovery after 21 hr. in 80 per cent sea water from two-cell 

 stage; //, differential conditioning in 90 per cent sea water 13 days; /, secondary modification 

 in Nile blue sulphate, initial concentration 1/1,000,000. 



in recovery after exposure to all inhibiting agents used, when inhibiting 

 action is not too great. The modifications resulting from differential tol- 

 erance or conditioning with continuous exposure to low ranges of inhibit- 



