Mast, Loeb's Mechanistic Conception of Life. ,"")Sf) 



if the form were not spherical, there would he more than one) 

 and that the limit to the number of embryos that can arise from 

 one egg "is not due to any preformation, but to other circum- 

 stances, the chief one being that with too small an amount of 

 protoplasm the formation of a blastula - from merely geometrical 

 reasons, as there must be a minimum size for the cleavage-cells - 

 becomes impossible." Neither of these conclusions seems to be 

 in accord with the facts. The experiments of Pfluger, Hertwig 

 and others show that when frog's eggs are flattened they still 

 develop into but one embryo; and the work of Conklin, in par- 

 ticular, shows that preformation in the egg has much to do with 

 the determination of the number of embryos that can develop from it. 



In this section then Loeb maintains that the form of organisms, 

 including the interrelation of different parts, is regulated directly 

 by the action of gravity, light, surface tension, etc. He rejects in 

 unmistakable terms, quoted above, the idea that natural selection 

 has anything to do with it. In another section however his whole 

 discussion of this problem is in complete harmony with the theory 

 of natural selection. 



In this section he postulates, under normal conditions, numerous 

 variations in form, structure and arrangement of parts' due to 

 hybridization and maintains that in a large percentage of the in- 

 dividuals which arise thus, these features are of such a nature that 

 they soon die leaving only those which are adapted to their environ- 

 ment. He says (p. 24): "The number of teleosts at present in 

 existence is about 10 000. If we accomplish all possible hybridiza- 

 tions 100 000 000 different crosses will result. Of these teleosts 

 only a very small proportion, namely about one one-hundreth or 

 1 per cent, can live ... It is, therefore, no exaggeration to state 

 that the number of species existing today is only an infinitely small 

 fraction of those which can and possibly occasionally do originate, 

 but which escape our notice because they cannot live and reproduce/' 

 The whole matter is summed up in the following startling sentence 

 (p. 25): - l Disharmonies and faulty attempts in nature are the rule, 

 harmonically developed systems the rare exception." No one to 

 my knowledge ever sketched the theory of natural selection with 

 bolder strokes. Loeb settles the whole question of adaptation and 

 the origin of species in the space of a few paragraphs. What is 

 more, he shows that all of these phenomena are only the product 

 of "blind forces". "Nobody doubts", he says, in concluding a brief 

 argument, (p. 26) "that the durable chemical elements are only the 

 product of blind forces. There is no reason for conceiving other- 

 wise the durable systems in living nature." 



Thus it appears that in this section in attempting to account 

 for morphogenesis, Loeb makes use of the fundamental principles 



