AXIAL SUSCEPTIBILITY GRADIENTS. 40! 



ectodermal disintegration occurs in three or four hours dis- 

 integration of the entoderm is usually not complete until one or 

 two hours later or in some cases even a longer time. 



By returning to sea water after the proper length of time in the 



reagent it is possible to stop death at any level of the body and 

 to bring about recovery and further development of the parts still 

 alive. In the blastula it is more or less of the basal portion which 

 remains alive, and this may close up and gastrulate, producing 

 dwarf gastruke with a disproportionately large enteron. In the 

 gastrula stage also partial dwarf gastrulse with large enteron 

 result from partial disintegration and recovery, because the more 

 apical ectoderm may be in large part destroyed while the basal 

 region of the gastrula and the entoderm remain intact. The 

 forms of larvae which develop from these partial basal blastulae 

 and gastrulae will be described in another paper. 



LATER STAGES. 



In the early stages of transformation into the pluteus, the 

 gastrula loses its apparent radial symmetry and becomes tri- 

 angular in outline in basal or anal view, the base of the triangle 

 representing the anterior region of the future pluteus. In side 

 view the apex of the gastrula is seen to be shifted toward the 

 anterior end as compared with earlier stages (cf. Figs. 19 and 16). 

 In the further transformation this apical region becomes the 

 oral lobe of the pluteus and the long anal arms develop from the, 

 basal region of the anterior end (Fig. 20). 



