CERTAIN GENERAL CKL'VRACTERISTICS 29 



the individual than those which it formed or would form without isola- 

 tion; but whether these represent more, or possibly in some cases less, of 

 the whole depends entirely on what we mean by "more" or ''less." For 

 example, when a short piece of a Tuhularia or Corymorpha stem develops 

 into only the extreme oral end of a hydranth or to two opposed oral ends 

 (pp. 334, 346), has it become more nearly a whole than it was originally? 

 Unquestionably, its developmental pattern has undergone alteration; but 

 what has occurred can scarcely be called a restitution, a reparation, a form 

 regulation, or even a regeneration in any strict sense. It is, however, a 

 reconstitution, but one which makes long-continued existence impossible. 

 It is perhaps even pertinent to raise the question whether continued dif- 

 ferentiation of an isolated part in the same way as without isolation may 

 not, at least in some cases, involve some reconstitution. The fact that 

 the isolated part is capable of more or less independent or self-differentia- 

 tion does not prove that it differentiated independently when not isolated. 

 In view of the experimental data the term "reconstitution" seems prefer- 

 able to any of the others used for this form of development, because it in- 

 volves no implications of approach to wholeness, regulation, or replace- 

 ment of missing parts. It implies nothing beyond alteration of develop- 

 mental pattern in the isolated part. As already noted, physiological or 

 physical isolation and reconstitution of parts occur in the various forms 

 of budding and fission. Either a new axiate pattern develops in a former 

 part of an individual, as in buds, or the partial pattern present undergoes 

 reconstitution, usually into the pattern of a whole. It is perhaps worth 

 pointing out that even embryonic development may be regarded as re- 

 constitutional in character. The egg and the spermatozoon are morpholog- 

 ically, and apparently also physiologically, highly differentiated and spe- 

 cialized cells, and in embryonic development the differentiation and pat- 

 tern undergo great alterations. For parthenogenetic eggs isolation from 

 the earlier organismic environment is sufficient to initiate development, 

 but in other eggs activation by the spermatozoon or by chemical agents 

 is also necessary. In any case the egg does not develop so long as it re- 

 mains as a part of the parent body in the ovarian environment. It is diffi- 

 cult to understand how anyone can observe the changes which egg and 

 spermatozoon undergo in fertilization and development and doubt or deny 

 the occurrence of dedifferentiation. If the gametes are, in any sense, parts 

 of the parent body during their development as gametes, embryonic de- 

 velopment is a more extreme reconstitution than any other form of de- 

 velopment. 



