146 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



gradient, has appeared, as apparently in annelids and also in echinoderms. 

 With outgrowth of the tail a very distinct reduction gradient appears in 

 it, the tip being the most rapidly reducing region of the larva; the neural 



Fig. 50, A-H. — Differential KMn04 reduction in larval development of the ascidian Corella 

 willmeriana, arrows indicating direction of progress. A, four-cell stage with basipetal decrease 

 in rate; B, C, gastrula in lateral and dorsal view; D, increase in rate of reduction in region of 

 future tail; E, caudal gradient with higher rate of reduction at tip than in any other part of 

 body and early reduction of scattered tunic cells; F, G, later stages of larval development; //, 

 caudal resorption about to begin (after Child, ig2yd). 



side of the larval body and the end reduce more rapidly than the other 

 side (Fig. 50, E, F, G). During its development the tail is also the most 

 susceptible region of the larva. In the full-grown larva the caudal reduc- 

 tion gradient is still distinct; but, as compared with the body, rate of 



