192 CHARLES R. STOCKARD 



instead of single bud formation. Patterson's description of the 

 origin of the quadruplet buds in the Texas armadillo furnishes the 

 most striking case in the study of these conditions. And we may 

 conclude that the budding or accessory embryo formation in the 

 egg of the armadillo is exactly the same developmental process 

 as that which gives rise to twins and double individuals in other 

 vertebrate eggs. 



However, the very important question yet remains to be an- 

 swered: Why does this accessory bud formation occur so con- 

 stantly in the Texas armadillo in contrast to the single embryo 

 formation of mammalian eggs in general? Patterson ('13) failed 

 entirely to answer this question, but he supplied some veiy sig- 

 nificant data which Newman ('17) has appreciated as being inti- 

 mately connected with the occurrence of polyembryony. 



In connection with the collection of material Patterson ('13) 

 discovered a 'period of quiescence' of the embryonic blastocyst. 

 Regarding this he states: ''The fact was first made apparent in 

 1911, when, after I had started collecting two weeks earlier than 

 in the preceding year, I failed to obtain the cleavage stages, al- 

 though judging from the condition of development in the vesicles 

 collected in previous years, one would naturally expect to find 

 these early stages during the period of my first collection in 1911." 

 The following year be began collecting still two weeks earlier 

 and again had a similar experience. "Practically all of these 

 vesicles lie free within the uterine cavity, either in the horizontal 

 groove or in the region of the attachment zone (placental area)." 



"It is evident from these data that the embryonic vesicle re- 

 mains for some time lying free "within the uterine cavity. Just 

 how long this period lasts, I am unable to state; for practically 

 every old female taken at the earliest date (October 15th) at 

 which I have collected, possesses a free blastocyst. How long 

 such blastocysts have been in the uterine cavity it is, of course 

 impossible to determine; but I should judge not very long, be- 

 cause two vesicles taken from the fallopian tubes show a develop- 

 ment almost as far advanced as that of some vesicles taken from 

 the proximal parts of the horizontal grooves. Taking all the facts 

 into consideration, I estimate the 'period of quiescence' to last 



