SECT. 3] AND ORGANISATION 597 



been obtained by various workers on Fundulus, and concluded that 

 in all cases the malformations produced most easily were those of 

 the fore brain, the head in general, the sense organs, especially 

 the eyes, the heart, the circulatory system, and the tail. These results 

 obviously fitted in very well with those appearing from the use of 

 the direct susceptibility method of Child, and this outcome of the 

 physiological gradient conception is perhaps one of its most attractive 

 aspects, for no other point of view serves to account for so many of 

 the facts of teratology. It was long ago pointed out by Dareste that 

 no relation seemed to exist between the application of a certain 

 physiological or physical condition and the resulting teratological 

 modification. Thus Herbst's "lithium larvae" and Stockard's "mag- 

 nesium embryos" have been shown to be obtainable with a great 

 variety of agents. There is, we may say, practically no specificity 

 in teratological action. "Any type of abnormality", as Bellamy puts 

 it, "may be produced under the influence of any inhibiting agent 

 by controlling the concentration or intensity of action, the length 

 of exposure, and the stage, i.e. physiological condition, of the Ggg 

 or embryo or parts of the egg or embryo when exposed." Since the 

 differences then do not reside in the teratological agents employed, 

 they must do so in the embryo itself — an admirably Kantian con- 

 clusion, which can only be explained on some basis which maps 

 out the embryo into a logical system. The only basis we have is the 

 conception of physiological gradients. It is difficult also to imagine 

 any other view which could explain such instances as the production 

 of the usual terata by fertilising eggs with foreign or injured sperma- 

 tozoa or treatment of the eggs before fertilisation as in the experi- 

 ments of Gee. Full discussions of the teratological literature and 

 interpretations of it from this physico-chemical standpoint will be 

 found for the fish embryo in the paper of Newman, for the chick 

 in the paper of Hyman, and for the frog in the paper of Bellamy. 

 It is very noteworthy that new teratological modifications not before 

 obtained have been predicted on the basis of physiological gradients, 

 and have afterwards been verified. 



Hyman next studied the gradients during the development of the 

 brook lamprey, Entosphenus appendix, an organism of considerable 

 interest, in view of the fact that, like the amphibia, the cyclostomes 

 are one of the three vertebrate groups which develop by holoblastic 

 unequal cleavage. Alcohol and acetic acid were used as the reagents 



