422 CM. CHILD 



portion of the preganglionic region, in the same solution which 

 brought about the earlier reduction of this region, and ten to 

 fourteen days later, that is, a month after the animals were 

 first placed in the solution, the heads range in form between fig- 

 ures 19 and 20. The whole head has undergone increase in size, 

 but the median region has grown much more rapidly than any 

 other part and has given rise to a disproportionately large pre- 

 ganglionic region. This region is functional and is bent and 

 twisted about in locomotion: it very evidently represents merely 

 an overdevelopment of the median preganglionic region with 

 its sensory margins. Its development can mean nothing else 

 than that the cells of the median region become, after a certain 

 length of time in the solution, more capable of growth than 

 those of the more lateral regions and that under these condi- 

 tions the median region grows to larger than normal size because 

 its ability to use nutritive material and to synthesize new pro- 

 toplasm is relatively greater as compared with that of lateral 

 regions, though actually of course less than in the normal animal. 

 In other words, the alteration of size and proportion means an 

 alteration in the metabolic relations of median and lateral re- 

 gions in consequence of differences in their susceptibihty and 

 capacity for acclimation. 



Animals with heads like figures 19 and 20, when removed 

 from the anesthetic solution to water, show a gradual approach 

 to the normal head-form. After two months in water some 

 heads may be nearly normal, but the preganglionic region is 

 usually still somewhat larger than normal. It is probable that 

 completely normal proportions would be reached in time, but 

 none of these experiments was continued longer than two months 

 after return to water. 



Differential accli^nation in development of new heads. When 

 pieces undergo reconstitution in alcohol (1.25 to 1.5 per cent) or 

 ether (0.2 to 0.4 per cent) or in low concentrations of chloretone 

 or of various other anesthetics, the development of the head is 

 at first markedly inhibited. A very common form of head under 

 such conditions is that shown in figure 22. Here the outgrowth 

 of new tissue at the cut surface is largely inhibited, but rediffer- 



