72 JOHN W. MACARTHUR. 



granularis and Strongylocentrotus lividus, that further descrip- 

 tion would hardly aid in our present purpose of analyzing and 

 interpreting the lithium effect. 



It is important to mention the production of practically typical 

 lithium embryos without the aid of lithium. Herbst found a good 

 substutute for the lithium salts in Na butyrate etc., and Driesch 

 ('95) obtained a high percentage of exogastrulae from develop- 

 ment at 30 C. for nearly a day preceding gastrulation. So it is 

 not entirely surprising to find that in CaCl?, N/8o to N/i6o, 

 often the majority of Strongylocentrotus eggs become character- 

 istic exogastrulae, etc. (and many of these fused twins) practically 

 indistinguishable in type from those in Figs. 1-3. Quite similar 

 exogastrulae are produced in Arbacia by NaCl, N/4 to N/8, and 

 in Strongylocentrotus by N/8 to N/2O NaCl. 



Asterias forbesii and Orthasterias sp. Starfishes are by no 

 means as responsive as the urchins and sand-dollar to the lithium 

 action. Though all characteristic stages of general inhibition are 



FIG. 8. Experimental Alterations of Aslcrias, a-e induced by LiCl, M/ioo to 

 M/i6o; m-p, induced by 75 per cent. sca-\vatcr; and q, by KNC, M/25,ooo 



