ORIGIN OF MONSTERS. II 431 



action 21 on the ovum of a female suffering from any of these 

 diseases may cause either its death and subsequent expulsion 

 or any conceivable monstrosity, the latter, if altering the tonic- 

 ity only of the blood, may by (osmotic) blastotomy produce 

 slight defects or duplication of the embryonic primordium and 

 thus in the latter case be responsible for the development of 

 monozygotic twins, or any monozygotic, more or less well 

 formed, 'symmetrical' duplicity. 



It might further be questioned whether the analysis of the 

 morphogenesis of our experimental fish duplicities as attempted 

 in the preceeding pages on the basis of FischePs theory is ap- 

 plicable to the higher vertebrates and mammals. 



Sobotta ('14) has already pointed out that while it is very 

 doubtful whether the first two blastomeres are equipotent and 

 totipotent in mammals it may be regarded as hazardous to 

 extend to the latter the conclusions reached regarding the 

 morphogenesis of duplicities in lower animals. However, oc- 

 casioned primarily by the recent researches of Fernandez ('09) 

 and Newman and Patterson ('10) and Patterson ('13) he suggests 

 hypothetically a stage (the ' embryonic blastomere' of the four- 

 celled stage) whose parts after the next cleavage might be 

 totipotent and thus capable of giving rise to monochorionic 

 double embryos if separated. 22 Undoubtedly, in view of the 

 meager data available for the earliest development in mammals, 

 generalizations must be made with extreme caution. Yet, 

 whatever the mammalian embryo-forming equivalent of the 

 ovum of amphibia (or other animals in which the first blasto- 

 meres are totipotent) may be, there is, as Fischel (I.e.) has al- 

 ready pointed out, no apparent reason to expect that its pros- 

 pective potency should be lower than that of the latter. 



21 Depending partly upon the 'maturation age' of the ovum at the time of its 

 fertilization. 



22 For Tatusia novemcincta, on which Patterson's ('13) investigations were 

 carried out, Sobotta assumes the separation of the four cells resulting from the 

 second cleavage of the hypothetical 'embryonic blastomere.' Pending further 

 investigations on the earliest stages of development in armadillo I should re- 

 gard as questionable the analogy between the polyembryony in the latter and the 

 occasional instances of 'twinning' in other mammals. 



