DIFFERENTIAL DEVELOPMENTAL MODIFICATION. II 239 



D or E. In D there is apparently re-ectodermization of the apical region, 

 but E appears to be completely anaxiate; and it may perhaps be ques- 

 tioned whether the external epithelium retains entodermal character or 

 has become ectoderm; it has undergone the decrease in thickness char- 

 acteristic of ectoderm. 



When entoderms of individuals in the condition of Figure 96, A and C, 

 come into contact, they tend to stick together ;'7 and large masses, con- 

 sisting of many individuals, often result. In these the entodermal regions 

 in contact gradually dissociate into the interior of the mass, and the 

 parts directly exposed to water become a continuous epithelium with the 



Fig. 96, A-E. — Dendraster, recovery after extreme inhibition. A, B, LiCl m/20, 9 hr. from 

 two-cell stage: A, 17 hr. water, B, 40 hr. water. C, LiCl m/20, 26 hr. from first cleavage. 

 D, E, LiCl m/20, 26 hr., 24 hr. water. 



apical regions at first protruding from the surface but gradually becoming 

 incorporated into it, so that finally a large vesicle full of cells results, with 

 complete loss of individuality of the component members. Within these 

 masses, however, numerous epithelial vesicles may develop after return 

 to water; they often persist free in the water after disintegration of indi- 

 viduals or multiple masses. The multiple forms are interesting cases of a 

 sort of reconstitution with more or less complete obliteration of axiate 

 pattern of the original individuals composing it and development of a 

 new individuality in which there is no evidence of anything but surface- 

 interior pattern. 



Secondary reconstitutional modifications of skeletal development in 



'" Less extremely inhibited exogastrulae often stick together by their entoderms if there is 

 loss of epithelial character at the tip, but they do not lose their individuality so completely as 

 the forms in which axiate pattern is almost obliterated. 



