232 J. S. HUXLEY. 



covery is thus lost by prolonging the treatment with poisons from 

 48 to 72 hours. 



4. Gastrulse killed by weak toxic solutions show differential 

 death, the enteron being more resistant than the rest of the tissues. 



5. In very weak solutions, progressive dedifferentiation of 

 plutei occurs. The arms are first resorbed, then the ciliated band 

 and oral lobe disappear, then the gut contracts. In early stages, 

 the trunk and aboral end are dilated, in later stages they are con- 

 tracted and the whole body is filled with cells. The process is 

 similar in all essentials to that seen in the dedifferentiation of the 

 Ascidian Clavellina. 



6. It could not be decided whether full recovery is possible for 

 plutei thus treated. Armless forms replaced in sea-water re- 

 mained alive and motile for 3^ to 4 weeks, and ingested diatoms. 

 Some of them showed further dedifferentiation in the sea-water, 

 finally reaching a spheroidal state, with spicules extremely re- 

 duced or absent, and gut reduced to a closed vesicle or vesicles. 



7. The process of dedifferentiation appears to be essentially 

 identical with that initiating metamorphosis and resulting in the 

 destruction of the larval organs in Echinoids. This is -probably 

 true also for metamorphosis in other groups. 



8. Echinoid metamorphosis, and possibly other types of meta- 

 morphosis also, would therefore appear to be initiated by dedif- 

 ferentiation-changes in the larval organs, not by autolysis or 

 phagocytosis, which are secondary phenomena. 



9. Ceteris paribus, tissues with large cell-surface are more sus 

 ceptible to unfavorable influences and more prone to dedifferentia- 

 tion than are those with a small area of surface per cell. 



10. The effect of mercury salts in dilute solutions is shown to 

 depend upon the total amount present as well as upon the concen- 

 tration. 



LITERATURE LIST. 



Child, C. M. 



'16 Experimental Control and Modification of Larval Development in the 

 Sea-urchin in Relation to Axial Gradients. Journ. Morph., 28, 1916, 

 P. 65. 

 Child, C. M. 



'15 Individuality in Organisms. Chicago Univ. Press, 1915- 



