DEDIFFERENTIATION IN ECHINUS LARVyE. 211 



the effect of dilute poisons on differential modification of growth, 

 and to compare the effects of cyanides and mercury salts. 



A. When fertilized Echinus eggs were placed in KCN 71/50,000 * 

 growth ceased at the 2- or 4-cell stage. A small percentage of 

 eggs were cytolysed and many had multiple asters and irregular 

 segmentation. In KCN ;?/ioo,ooo, after 24 hours more eggs were 

 cytolysed, a certain proportion had got no further than the 2- or 

 4-cell stage, and a small percentage had become blastulse, most of 

 them of the abnormal solid type (stereoblastulse). The controls 

 had in the same period reached the gastrula stage. 



After 72 hours, 24 hours after the controls had reached the 

 early pluteus stage, these blastulse had become late gastrulse. 

 These were transferred to sea-water, and developed as far as the 

 pre-pluteus stage, but never became normal plutei, thus bearing 

 out Child's conclusions that considerable poisoning in the early 

 stages in some way disturbs the relations of parts so that even 

 when the developing organism is replaced in normal conditions, it 

 can only develop up to a certain stage, and no further. 



In this connection the observations of Perkins ('02) are of 

 interest. He discovered that the hydriform larva of Gonionemus 

 when kept in the laboratory lost its typical form and assumed an 

 irregular amceboid shape. It moved about, apparently ingested 

 food, repeatedly underwent a form of fission, and lived for over 

 2 months. 



Obviously, therefore, viability and capacity to develop are by 

 no means synonymous, and we have the theoretical possibility of 

 the existence of persistent larval forms due to unfavorable con- 

 ditions as well as to genetic variations. 



Other larvae were replaced from KCN n/ioo,ooo to sea-water 

 at 48 hours, from the blastula stage. After a further 48 hours, 

 many had formed early plutei. These were mostly of a very 

 wide-angled type (Fig. 9), thus showing what Child finds in 

 similar circumstances, and has called " differential recovery." 



Thus between the 48th and the 72nd hour in the solution the 

 larvae had lost their power of recovery in sea-water, though not 

 of continued existence. 



i The molecular concentration is simply given for convenience : the actual 

 ionic concentration of CN would naturally vary with the hydrogen-ion con- 

 centration and other factors of the sea-water used. 



