EXOGASTRfLATION AXD RELATED MODIFICATION-. 85 



the most basal parts of the gut are most increased, as the lithium 

 alteration becomes maximal. 



3. In the lithium larvae the order of direct susceptibility of 

 parts to quickly killing agents is essentially the reverse of that 

 of the normal v;a-trula and larva: the gradient of susceptibility 

 in the normal e.ui; and blastula is apico-basal, and declines from 

 tin- e< loderm tn <-nti.<lerm and mesenchyme in the -a-trula and 

 larva, while in the fully formed exogastrula the susceptibility of 

 tin- ( tixli-nn 'LM-trula wall) is least, that of the entodermal 

 parts more, and that of the mesenchyme probably greate-t of all. 

 A -iniilar iv\ei-al of the usual susceptibility is met with in pan- 

 of the differentiated gut of the lithium larva. 



4. " Lithium larvae" are not the specific product of the I.i' ion 

 alone, but are readily obtained in CaCl, diluted or Male 

 \\.iter, by Na butyrate (Herbst), by heat (Drieschj, and in less 

 typieal t'orm by many other salts, basic dyes, etc. 



5. The specificity resides rather in the biological material 

 than in the agent, but Li' appears to possess in high d the 

 pi.\\er of locali/ed action : i.e., its inhibition is markedly rej i> mal. 

 >lo\\in- down or stopping development of the most apical pan-, 

 while hindering little or inappreciably development of the lu-al 

 parts. 



induced, highly differential, rates of growth and 

 diiii -rentiation lead directly or indirectly to exoga>ti ulatimi in 

 e\tt( in. . ases; perhaps largely because of the nuvhaniral im; 

 Ml'ilitx "! invaginating a greatly enlarged entodenn intu an 

 umiMially Mnall Mastocoel, itself overcrowded \>\ a pn ous 

 ami exi ess pu'lileration of mesenchyme. 



7. I'lieM- ( -liaii^es in proportions and ) n >-it i< ui> of part- in 

 " lithium rniln \ os" appear to follow as naturally and ne. .---arily 

 from the altered metabolic relation- ni"iv or 1( inph -te 



reversal of the physiological gradients - Hie normal prop,, ni..n- 

 and positions of part> follo\\ in. in the normal metal xilir relations. 



BIBLIOGRAPHY. 



Bataillon. 



'01 La Pressure Osiiiotit|ii. i-t !. -s grandes Problcint^ dc la B .. f. 



Entw. Mrdi; XL. i 

 '04 Lc- ' rr. ex- 



prriiiu-tualfs. Arch. f. Km\v. Mivh.. X\'III. 



