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Conklin.] *^^ [May 1, 



even be that the position of the blood vessels is not so represented, but 

 there must be some ultimate cause back in the germinal plasm itself 

 •which determines the series of causes which finally produces the color 

 paterns. In short, this feature, like most others, was predetermined 

 from the beginning. 



(2) Herbst * has shown in a series of interesting experiments that bj^ 

 tlie use of various chemical substances the development of echinoderms 

 may be profoundly modified. For example, in sea water deficient in 

 calcium-chloride, or in which there is an excess of potassium-chloride, 

 the pluteus larva, instead of developing calcareous spicules and the long 

 ciliated arms which give the normal larva an angular, easel-shaped 

 appearance, remains rounded in shape much like the larva of Balano- 

 glossus, in which no spicular skeleton is developed. The withdrawal, 

 therefore, of certain normally present substances from the environment 

 may profoundly modify the end result. But in this case, as in the 

 other, it is absolutely certain that the calcareous spicules were prede- 

 termined in the egg cell, although in the absence of calcareous matter 

 from the water those spicules could not be built — the plan was there, 

 but the building material was lacking. 



Such modifications resulting from unusual conditions of pressure, 

 temperature, density, nutrition — in fact, any alteration of the chemical 

 or physical environment — may appear in any stage of development 

 from the unsegmented egg to the adult condition, but it must not be 

 supposed that the entire development can be reduced to such factors. 

 Loeb argues that we do not inherit our body heat from our parents 

 ))ecause it depends upon certain chemical processes, but is it not abso- 

 lutely certain that we inherit a certain protoplasmic structure which 

 determines those chemical processes, and hence the body temperature ': 

 To assume that extrinsic causes determine whether there shall hatch 

 from an egg a chicken or an eagle is the sheerest nonsense. The study 

 of extrinsic factors in relation to inheritance will serve to simplify some 

 of the intricate problems to be explained, but surely no one believes 

 that development can ever be referred entirely to such factors. The 

 lact is that determinism, which is the most fundamental characteristic 

 of inheritance, is manifested at every step of development, and there is 

 certaiily no escape from the conclusion that this determinism depends 

 upon protoplasmic structure, and that this structure it is which is trans- 

 mitted from generation to generation and which forms the physical 

 basis of inheritance. 



All really inherited characters must, therefore, be represented in 

 the structure of the germinal protoplasm, and must consequently be 

 ])resent from the beginning of development. " We must consider it as 

 a law derivable from the causality principle," saysllatschek,t "that in 



*Zeit. wiss. ZooL, Bd. Iv. 



t Berthold Hatschek, Vcber die EntuickluJigsgtschichlc von Teredo, Arb. Zool. Inst., 

 Wicn, 18S0. 



