Genie Control of Development 325 



and probably in most invertebrates in which the series of embryonic 

 determinations under genie control takes place in the respective 

 areas of the egg and embryo directly (the mosaic type of develop- 

 ment). Though we mentioned some of Brachet's work in Amphibia, 

 this was done only in a general way. However, our problem of genie 

 activation appears also in the case of the vertebrate egg (and some 

 insects) where the inductor type of embryonic determination (Spe- 

 mann's "organizer") is found. 



In order to realize the basic difference, we may point out first the 

 results of intergeneric (etc.) transplantation of the inductor tissue 

 (assuming the basic features of this work since Spemann to be 

 known). If frog gastrula ectoderm is transplanted into a Triton gas- 

 trula, the Triton "organizer" makes this group of cells differentiate 

 according to its position, for example, into mouth parts. However, 

 these are typical frog parts, with a sucker and horn teeth, neither 

 existing in Triton. Thus the genetic condition of the cells, that is, their 

 genie material, controls differentiation, though the clearly unspecific 

 inductor starts the general features of development. These famous 

 experiments show clearly that the inductor action upon development 

 is basically different from genie control of development. However, 

 the generalized action of the inductor (in the foregoing example, 

 Spemann spoke of the order given to produce mouth parts) must in 

 the end also be under genie control. Thus we may expect an insight 

 into the problems under discussion from a further analysis of induc- 

 tion. 



The first important set of facts is the successful induction of 

 axial structures by transplanted bits of any tissue taken from all 

 kinds of animals. Then it turned out that the same tissues after being 

 killed by different procedures also acted as inductors. This was fol- 

 lowed by the proof that parts of the amphibian gastrula which, if 

 transplanted, do not act as inductors will become inductors when killed 

 first. It became obvious that there is no "organizer," but that induction 

 must be due to the presence, or production, or release of a substance 

 of rather general distribution. 



The search for such substances, mainly by the schools of Needham- 

 Waddington, Brachet, Spemann-Fischer, Barth, and Holtfreter (see 

 Brachet, 1950a; Holtfreter, 1951) led to great confusion: Needham and 

 Waddington believed that they had proved certain sterol compounds to 

 be the active substance. Fischer could not confirm this, but found 

 that certain acids, among them DNA, gave positive results if put into 

 the gastrula. Barth again differed and considered protein extracts 



