JOHN W. MACARTHUR. 



gastrular wall and more fully divided gut; and in their larger 

 oral region and occasional belated evagination of the stomadeum. 



N/25O LiCl yields mostly ordinary forms, but little retarded, 

 and only 5-10 per cent, exogastrula?. In still loxver concentra- 

 tions development quickly approaches that of the controls. 



Other agents, such as KXC, CuSO,, HgCl 2) HC1, CaCl 2 , XaCl, 

 and conditions, such as diluted or staling water, used in appro- 

 priate concentrations and intensities, were found to cause the 

 same sort of general inhibition of development as LiCl, stopping 

 entogenetic changes at cleavage, blast ula, or gastrula stages; all 

 may be employed to show the relatively greater inhibitory effect 

 on apical and ectodermal parts; many brought the blastula up to 

 a stage (Fig. 5) precisely simulating late Lithium blastulae; and a 

 few produced a small percentage of imperfect exogastrulae, as 

 in Fig. 5. 



Arbacia pimctulata and Strongylocentrotus franciscana. In 

 these sea-urchins a range of types of abnormality was produced 



d 



FIG. 6. Exogastruhr, Constriction Forms, and Double Emluyn t .\rhacia, 

 produced by LiCl and XaCl. a-g from LiCl, M/8o to M/ioo; It j, I'min N'aCl, 

 M/4 to M/8. 



