212 J. S. HUXLEY. 



B. HgCl,. /5,ooo, n/io,ooo, n/2O,ooo, 3-1/50,000 and 72/100,000 

 solutions allowed segmentation to proceed to the 2-, 4-, or 8-cell 

 stag'e in 24 hours (mostly to the 4-cell stage). Many segmenting 

 eggs, however, were obviously damaged, and by 48 hours all were 

 dead. The course of events was similar in a w/2OO,ooo solution, 

 except that by 24 hours segmentation had proceeded to the 4- to 

 32-cell stage (mostly to the 8-cell stage). Transference from 

 n/ioo,ooo and 72/200,000 to sea-water at 24 hours had no effect, all 

 being dead at 48 hours. The dead blastomeres were well-pre- 

 served, not cytolysed or disintegrated. 



As the solutions used were obviously too strong, 24-hour gas- 

 trulae from the control were placed in n/5oo,ooo and n/ 1,000,000 

 solutions. These too were all dead 24 hours later (48 hours 

 from fertilization) ; but they showed the interesting phenomenon 

 of differential disintegration. All the tissues except the archen- 

 teron had entirely disintegrated, and lay as a sheet of cell-debris 

 on the bottom of the vessel. The archenteron, on the other hand, 

 was well preserved, and the outlines of its walls could be clearly 

 seen (Fig. 10). The spicules were usually to be seen adherent 

 to it. Sometimes it appeared solid. This is obviously an occur- 

 rence of the nature of those observed by Child ('15), and utilized 

 by him in his axial gradient theory. 



3. DEDIFFERENTIATION OF LARVJE. 

 Unfortunatelv no further Echinus were to be had. and I was 



-- ' 



therefore unable to repeat the experiments with more suitable 

 strengths of solution. Wishing, however, to see what the effect 

 of poisons might be on more advanced stages, I transferred some 

 of the plutei from the controls to various solutions of KCN and 

 HgCl 2 . The most interesting results were obtained in the mer- 

 curic-chloride solutions. 



C. A preliminary experiment was made with 2-day plutei in 

 HgCl 2 n/i, 250,000. After 6 hours, many showed a retraction of 

 the arms, leaving part of the skeletal spicules protruding. After 

 24 hours, many had died. The following types could be distin- 

 guished : 



i. Partially dead, with disintegration of the tissue of the arms; 

 the aboral ectoderm not disintegrated, or with a few cells migrated 



