DIFFERENTIAL DEVELOPMENTAL MODIFICATION. II 243 



mental data on developmental modification and metabolism in the sea 

 urchin. They have described effects of various agents and of absence of 

 the sulphate ion and from these experiments have drawn certain conclu- 

 sions concerning metabolism.^' As regards some of this work, it is diffi- 

 cult to resist the impression that the experimental data do not always 

 provide an entirely adequate basis for the hypotheses advanced. Only a 

 few points of these investigations can be touched on here. Accepting 

 Runnstrom's hypothesis of two opposed, overlapping gradients, Lindahl 

 and his co-workers present various lines of evidence which they regard 

 as justifying the conclusion that the 

 metabolisms of animal and vegetal 

 regions differ specifically in character. 

 Certain agents are believed to "ani- 

 mahze," that is, to increase and ex- 

 tend the animal kind of metabolism; 

 certain others, to "vegetativize" (veg- 

 etalize). Here, also, the possibility 

 of differential tolerance, conditioning, 

 or recovery is apparently not recog- 

 nized, although it is noted incidental- 

 ly that further modification of form 

 may occur after return to water. 



Perhaps the most interesting of 

 the modifications described are the 

 animalized larvae obtained by ex- 

 posure of eggs before fertilization to 

 NaSCN in calcium-free sea water, 

 also to Nal and sometimes by expo- 

 sure to calcium-free sea water alone, with fertilization and develop- 

 ment in natural sea water. The animalized larvae are without entoderm 

 or mesenchyme, that is, entirely ectodermal; and in the more extreme 

 types the long cilia normally appearing as a group or tuft about the apical 

 pole in certain earlier stages develop over much or all of the surface of 

 the blastula-like forms (Fig. 97). The cells bearing the long cilia also be- 

 come different from the general ectodermal epithelium and similar to cells 

 of the apical tuft. These forms do not develop beyond the stage of ciliated 

 blastula-like larvae, though they lose their long cilia in later stages. This 

 modification is prevented by exposure to cyanide or to lithium after fer- 



^' Lindahl, 1933, 1935, 1936; Lindahl and Stordal, 1937; Lindahl and Ohman, 1938. 



Fig. 97. Faracentrotus lividus. — In iso- 

 tonic NaSCN (5 cc. NaSCN, 100 cc. sea 

 water) for 18 hr. before fertilization; fer- 

 tilization and 32 hr. development in sea 

 water (from Lindahl, 1936). 



