PRODUCTION OF MONSTERS BY HYBRIDIZATION. 3! I 



for the development of isolated eyes and hearts in other embryos 

 of the same series, which are treated exactly as those were in 

 which the eyes were suppressed or the heart failed to develop. 



It will be seen that both Stockard and Werber believe that 

 abnormal development is the result of toxic or deleterious 

 substances introduced into the egg from without. It has been 

 shown however that identical results can be obtained by purely 

 physical methods. 



In a very recent paper Kellicott ('16) has reported the pro- 

 duction of every known type of teratomata in Fnndulus by 

 merely subjecting very young embryos to low temperatures. 

 Eggs placed in the refrigerator a few minutes after insemination 

 very nearly stopped development and some apparently under- 

 went regressive changes. When returned to normal tempera- 

 tures these eggs developed nearly every type of abnormality. 

 The most frequent terata were those of the eyes and of the 

 heart. A list of terata would be a mere repetition of those 

 obtained by other methods. 



By way of a theory of the genesis of monsters Kellicott pro- 

 poses what he calls a " disorganizational hypothesis," namely 

 "that the cause of abnormal and monstrous development, is to 

 be found in a disturbance of the normal organization of the 

 ovum, as expressed by the unusual character and distributions 

 of the differentiated materials of the egg protoplasm." It should 

 be noted in connection with these low temperature experiments 

 that the first result is a very pronounced lowering of develop- 

 mental rate, amounting in some cases almost to a cessation of 

 development, accompanied by certain regressive changes. There 

 is also in all cases a permanent retardation even after the em- 

 bryos are returned to normal temperatures. It seems then 

 that the primary effect of low temperature is the lowering of meta- 

 bolic rate. 



It will now readily be seen that the whole series of teratomata 

 in fish eggs may be produced in three entirely different ways, 

 the results being the same in each : 



1. By the use of chemicals whose action is such as to lower the 

 rate of metabolism. 



jfi 



2. By means of low temperatures, which $ffect^ directly the 

 rate of metabolism. 



