206 LIFE: ITS NATURE AND ORIGIN 



unspecific, as in the hormonic type) which diffuses through the cyto- 

 plasm to the place of its form-controlling action." Owing to the 

 complex nature of the resulting umbrella, the formative material may 

 consist of several substances; or a substance with several catalytic 

 potencies; or else it must initiate in the cytoplasm of both species the 

 same "entelechy" of catalyst formation and chemical change. 



After describing Hammerling's work, Needham states: "From 

 all that has been said in the preceding sections, it will have become 

 clear that the genes act in development by producing, inhibiting 

 the production of, or masking and unmasking, hormones, cata- 

 lysts or inhibitors in more or less diffusible states. Hence their 

 undoubted effects upon rates of reaction in the embryo. It might 

 even be said that the main difference between genetics and embry- 

 ology is that in the former study only those inductors are described 

 which are unable to pass through the cell-membranes of the cells 

 in ivhich they are formed, while in the latter, only inductors of a 

 more diffusible nature are described. But this would leave out 

 the whole question of competence, which is likely to remain 

 mysterious long after our present knowledge of genes and in- 

 ductors has quadrupled its present state." 



It is strange that Needham should see such mystery in compe- 

 tence, which he defines as "the state of reactivity of a part of an 

 embryo, enabling it to react to a given morphogenetic stimulus 

 by determination and differentiation in a given direction." As 

 pointed out above, the formation or activation of specific cata- 

 lysts will commonly call upon local tissues to bear some part of 

 the burden, e.g., by supplying carriers, prosthetic groups, elutors, 

 or suitable pH; and if the prosthetic group should find the es- 

 sential carrier already preempted by some other group, the pros- 

 pective catalyst may not be formed. By blocking one reaction in 

 a catalytic chain, the absence of a single catalyst may alter the 

 local chemical output, and therefore the formation of substances 

 and structures which are criteria of physiology as well as of de- 

 termination and differentiation. 



Some Abormalities 



Let us now consider some of the consequences which may fol- 

 low if the usual course of catalytically directed chemical change 

 is upset. The normal catalyst entelechy is all askew. 



First come the naturally occurring abnormalities termed teratomata, 

 defined as a group of histologically differentiated tissues (often 



