224 



HUXLEY - 



Gonioncmus observed by Perkins ('02) should again be men- 

 tioned here. 



As regards parts of organisms, attention may be called to the 

 phenomena seen in sponges (Minchin, 'oo, p. 29). When an As- 

 con type of sponge contracts, the internal environment is altered, 

 and the collar cells are unable to maintain their typical form, los- 

 ing their collar and flagellum and becoming spheroidal. See 

 also Huxley ('21 a, p. 313). 



The familiar resorption of many grafted tissues may also be 

 mentioned. Muscle fibers, like Clavellina, also dedifferentiate 

 preparatory to regeneration when cut across. (Towle ('01).) 



Even the form of mental organization is subject to the same 

 limitation. In certain " shell-shock " and other cases, strain and 

 unfavorable environment render the higher part of the mental 

 organization unable to maintain itself, resulting in what is known 

 as regression. See Nichol ('20). 



We may thus say that maintenance of normal form is possible 

 only in certain environments. Certain stimuli result in what may 

 be called hyper-typical form: e.g., in regenerating Planarians, 

 high temperature produces forms with exaggerated heads (Lillie 

 and Knowlton, '97 ; Child, '15, p. 138). On the other hand, many 

 unfavorable stimuli do not permit the establishment of the type 

 at all : they result in infra-typical form e.g., cold in regenerating 

 Planarians; below a certain temperature, no head is formed (auctt: 

 cit.). 



B. Dedifferentiation and Metamorphosis. 



The resemblance of the phenomena here described to those oc- 

 curring at the metamorphosis of the pluteus is very striking. Ac- 

 cording to MacBride ('02) the course of the process is as follows: 

 The larva sinks to the bottom, presumably as a direct result of the 

 weight of the growing Echinus rudiment. The arms are next 

 resorbed, those on the same side as the Echinus rudiment first. 

 The larval oesophagus contracts. The ectoderm of the ciliated 

 epaulettes is " invaginated " and devoured by amcebocytes (the 

 description, however, does not negative the possibility that the 

 cells of the epaulettes may migrate out of the tissues, rather than 

 amcebocytes migrate in). During arm-resorption, the ectoderm 



