326 C. M. CHILD. 



in alcohol 1.5 per cent, for 48 hours after section and then re- 

 moved to water; fifty similar pieces were placed in water for con- 

 trol. Results are in percentages. 



Normal. Teratoph- Terato- Anoph- Headless. Dead, 



thalmic. morphic. thalmic. 



Ale. 48 hrs 14 16 8 18 38 6 



Water 20 44 2 26 8 o 



A much larger percentage of headless forms appears in alcohol 

 than in water. 



5. Complications in the Effects of Depressing Agents and Con- 

 ditions. 



In the present paper I wish merely to record the fact that under 

 certain conditions and within certain limits depressing factors 

 increase the head-forming capacity in pieces, instead of decreasing 

 it. As I shall show elsewhere, this result can be accounted for 

 without difficulty. It depends largely upon the fact that the 

 rate of metabolism in the cells at the anterior end of the piece 

 which react to the wound increases in the course of this reaction, 

 while that of more posterior regions of the piece remains essen- 

 tially the same. The depressing factor decreases the rate in 

 both regions and with a certain degree of depression the 

 more posterior region will become almost quiescent while the 

 anterior region which loses its previous differentiation in conse- 

 quence of the wound reaction will still be active. Under these 

 conditions the dominance of the anterior over the posterior region 

 will be increased and a larger percentage of heads may be formed 

 in spite of the depressing effect, simply because the anterior 

 region is more capable of living, growing and differentiating at 

 the expense of the posterior region. Under these conditions 

 then the depressing effect will appear to be a morphogenic 



stimulus. 



6. Mechanical Stimulation. 



As is well known, the shorter pieces of the planarian body, 

 especially those from the more posterior regions of the first 

 zooid, very commonly move about but little until regulation 

 has attained a certain stage; after this stage "spontaneous" 

 movements occur. Larger pieces show these movements at 



