ir ORGANOGENESIS 735 



Gluecksohn-Waelsch, 1954, 1953), of the chick (Gluecksohn-Waelsch, 1953) and 

 to a less extent of other forms. Most of these studies are conclusive only at the 

 ■descriptive level, but valuable information is available from analysis of these 

 studies. The time of primary genie action in the mouse, for example, varies from 

 the preimplantation stages to the time of initiation of the metanephric kidney at 

 about 12 days. Of particular interest, of course, is the syndrome of effects ap- 

 parently caused by a single gene. For example, the effects on the urogenital and 

 skeletal system result from a single dominant mutation (Sd) and here only when 

 present against certain genetic backgrounds. Gluecksohn-Schoenheimer (1949) 

 relates the action of Kink to "organizer phenomena" in the mouse. The literature 

 on the genetic dependence of blood antigens is rich (see Irwin, 1955). Schechtman 

 (1955) reviewing the nature of blood antigens particularly in the chick and 

 mammals, assembles convincing data which reiterate genetic dependence and 

 points out the epigenetic nature of development of blood antigens. He concludes 

 that they are end-products of differentiation, and as such, are not mechanisms of 

 differentiation. Telfer and Williams (1953) find that "the blood antigens of the 

 Cecropia silkworm undergo changes which are closely correlated with the morpho- 

 genetic events comprising metamorphosis." 



It is appropriate to close this section with a quotation from the father of 

 physiological genetics, Richard Goldschmidt (1955): "The type of penetrating 

 analysis of development and growth just reported leaves the geneticist where he 

 was, specifically where I was in my book of 1927: development consists of a series 

 of hierarchical subdivisions of the embryonic material in regard to its intimate 

 chemistry, a subdivision or stratification which is the consequence of the physical 

 and chemical properties of the whole system and its subsystems. The stratification, 

 an automatic outcome of the genically controlled syntheses of different substances 

 and the direction, order, and place of the genically produced prompters of 

 stratifications, provides the competent material for more and more restricted 

 genie action, otherwise called the activation of the genes, which works mainly 

 by influencing rate processes. Only then do the secondary effects under genie 

 control by means of specific enzymes, hormones, and auxins, and also through 

 contacts, set in. It does not help much if we express any or all of these steps in 

 terms of plasmagenes, macromolecules, and templates. In view of our ignorance 

 about what really happens, the old-fashioned general description is still adequate. 

 This, however, does not mean that, within that frame, more specific notions 

 cannot be developed. We are all anxious to see that done." 



3. Energy Sources of Development 



a. General. Bohr and Hasselbalch (1903) found a correspondence within 4% 

 between heat produced by the developing chick and heat loss expected from 

 respiratory measurements. Smith (1946) in the trout found a precise balance 

 between energy available in the egg and that available from the hatched embryo 

 plus measured heat loss. As Weiss (1953b) points out "Developmental phenomena 

 do not violate the laws of thermodynamics" and Butler (1946) after an analysis 

 of the same question, concludes: "Thus there is no outstanding difficulty in 



Literature p. 744 



