34 Henriksen, A Functions! view of Development. 



stages seem offen to be so firm thai a longer period is necessayy 

 for each blastomere to adjust itself as an independent whole. 



Let us first take an illustration from exj)eriments done on 

 isolated blastomeres from the earlier cleavages of the ctenophöre. 

 It has been demonstrated that isolated blastomeres of two, four 

 and eigbt celled stages of many im ins undergo at first a cleavage 

 as they would have done if forming a part of a complete embryo 

 and give rise to defective larvae having only four, two or one 

 swimming plate. But another question arises in this connection, 

 namely, in how far is the equilibrium of the species established in 

 this case. and we get the surprising result that althoügh these 

 swimming plates are reduced in number the larva is fitted for its 

 funetion in lue. It possesses all the parts of the embryo except 

 the reduction in number, but the amount of growth energy is 

 distributed among these parts; so the potentialities present are not 

 sufficient to produce an adult animal. 



If the blastomeres of the frog in a two-celled stage are isola- 

 ted they may give rise to a typical half-morula and half-gastrula 

 yet finally produce a perfect larva, this seems to show that the 

 relation of the blastomeres were quite firmly formed to suit their 

 companionship in the development of the organism but when 

 separated was able, by degrees, to return to the equilibrium of 

 the species, so as to form perfect larvae and even here the proof 

 seems to be that we had no preformation of either half but only 

 that relations within the blastomeres were more firmly established. 

 But it should be remarked that the position in which the blasto- 

 mere were flept had much to do with the results, so who knows what 

 external influences may do in certain cases. As we soon will see 

 from Prof. J. Loeb's experiments, even a slight charige may have 

 the most disastrous result for the future embryo. 



Another illustration of this nature is that of Prof. E. B. 

 Wilson on isolated blastomeres of the Dentalium. Here the 

 relation within the blastomeres were firmly established and I be- 

 lieve he states that they all give rise to defective larvae, but the 

 smaller half by far the greater difficulty has to establish the proper 

 relations, due without doubt to the fact that it possesses less 

 growth energy and slightly different relations. 



Even the above illustrations which I think are the most striking 

 in favor of the theory of preformation of the embryo in the .egg 

 in some form of microcosm gives us no basis for such conclusions. 

 The only way we can interpret such results is as given above, 

 that we have such relations within the egg, blastomeres, and all 

 cells. It becomes a necessary conclusion drawn from the facts of 

 embryology as I have already shown. 



That these relations within the egg are more firmly established 

 in some cases than in others is not surprising but the fact that 

 each blastomere will tend do develop as a complete larva shows 

 its independence when liberated, and we should not forget that 

 any experiment will naturally introduce a more or less deseased 



