io8 THE PHYSIOLOGY OF TWINNING 



THE FISSION THEORY VERSUS THE BUDDING THEORY 

 or TWINNING IN THE ARMADILLO 



At the present time two writers, Patterson and 

 Stockard, hold to the budding theory, while Assheton 

 and the writer feel that the process is not one of budding 

 but of fission. Assheton says: ''One cannot have 

 budding unless there is a stock from which budding 

 takes place. There is nothing in Tatusia {Dasypus) on.Q 

 can call a stock. The phenomenon is clearly that of 

 fission." To this Stockard replies: ''The use of the 

 word bud or budding in connection with double embryo- 

 formations as employed by Patterson (1914) has been 

 criticized by Assheton, who suggests fission as the better 

 word for the process. Such a discussion seems devoid 

 of value and I employ the word bud to mean what is 

 indicated above." 



It is evident from this expression of Stockard's that 

 he regards the distinction between budding and fission 

 as a valueless splitting of hairs. I feel quite the opposite. 

 To me the interpretation of armadillo twinning as a 

 budding process is extremely misleading and involves a 

 total misapprehension of the significance of the nature 

 of twinning. In order that we may be on solid ground 

 in this discussion it becomes necessary to re-examine in 

 detail the actual facts upon which the theories of twinning 

 are based. We are indebted to Patterson for his excellent 

 description of the facts. It is only his interpretations 

 that seem to me to be incorrect. 



The armadillo blastocyst, just before it shows 

 morphological evidences of twinning, is represented in 

 Figure 46. It is now connected with the maternal 

 mucosa by means of the Trager ring. Cell division has 



