KX<>i.\-I Kll ATIOX AND RELATED MODIFICATION-. 79 



(b) Ilvperlrophy of entodermal parts, especially basally: 

 Relative and ab-olute increase of size of the gut in general, and of 



the fore-gut in particular (Figs' 2, 3, 4 etc.). 

 Thickne of eiit< -dermal wall (p. 68). 

 Kiclim--- of entoderm in nuclei (p. 68). 

 Small size of ntodermal cells (Herbst; for frog, Bellamy '19). 



(c) Rein/in- and Absolute Diminution of the Ectoderm, especially 

 a pic ally: 



Reduction of the ectodermal component of the hour glass forms 



(Figs. 2, 3). 



K- 'anlation of the apical region in differentiation (p. 69). 

 !' 'ention of radial symmetry (p. 69). 



! sen ess in nuclei (Herbst). 

 Large si/.e of ectodermal cells (Herbst, Bellamy. Le Plat, '20, 



et al.). 



I ilure of ectoderm to grow down over the entoderm in the I 

 (Gurwitsch, '94, Morgan, '(.>3/>, Bellamy. 'i<). Le Plat, '20). 



Since the main object of this paper is to deal with the lithium 

 eiiect physiologically, it will profit to restate the morphological 

 i just summarized in physiological terms: 



Sufficiently strong concentrations of the Li ion will suppress 

 dc\ t lopment at any early or late stage of cleavage, of' the blast ula, 

 etc. Slightly lower concentrations also retard development, but 

 this retarding influence is most marked in the most su-ceptible 

 'derm) of the embryo, distinctly less marked in tin- le-- 

 -n-tepiible entoderm. and least marked in the lea-t -u-( -f|H ililc 

 mrsi'in -li\ inc. The last tissur undergoes a rel.ilix i-l\- rapid and 

 rxivssive growth and abundant proliferation (in niaiu \\ 

 resembling malignant tumor growth) to till the blastoccele and 

 lay down the anlage of an increased number <>| ~kelet.il -pit nle- 

 (which at once push out the arm- of the plnten- it recovery i~ 

 permitted). The change of position <,f the me-en< h\me ma\ in- 

 dicate a tendency (active or pa--i\ to or.-upy ell- 

 of lowest metabolic activity. 



The entoderm growth zone extend- it-elf apirally on t> the 

 gastrula wall (more and more as the ^r.idiein i- le\dK-<| do\\n or 

 reversed) by virtue of an enhanced mitoijc ,md m<p\\th activity, 

 \\hich is one of the most distinctive character- of a lithium embryo 



