STEUCTURE AND DEVELOPMENTAL RATE 195 



armadillo egg itself is highly disposed toward the formation of 

 accessory embryonic buds. 



There is the possibility, of course, that this natural experiment 

 with the armadillo egg has become so exactly regulated as to 

 influence the developmental processes precisely the same way 

 each time, yet this is highly improbable for several reasons. 

 The armadillo egg is not a case of simple twin growths from the 

 blastoderm, but, as Patterson finds, there are primarily two buds, 

 and then very promptly two secondary ones arise making the 

 four, and after this the budding process ceases. In the South 

 American species, however, it would appear as though a tertiary 

 budding occurred giving the usual eight embryos; and in rare 

 cases still another budding occurs from a few of the existing buds, 

 giving a total of as many as twelve. It would certainly seem as 

 though the blastoderm in these species passes through a stage of 

 agametic reproduction or budding of a nature unknown among 

 other higher vertebrates. But the possibihty for such expression 

 might only exist on account of the delay in implantation of the 

 blastocyst and consequent shortage of the oxygen supply neces- 

 sary for the rapid formation and growth of the single embryo. 



It is important to keep in mind that there are species of the 

 armadillo which produce only a single offspring from one egg. 

 It is not known whether their embryos have a 'period of quies- 

 cence,' but if they have the period either occurs at a different 

 developmental stage or the egg does not possess the inherent 

 budding tendency of the other species. 



It remains now to account for the fact that although the egg 

 of the deer has a 'period of quiescence' during its development it 

 does not give rise with any degree of frequency to twin indi- 

 viduals. In the first place, it is entirely uncertain from the scanty 

 accounts as to what time in development the quiescent period 

 occurs. Assuming that such a period does exist, it might occur at 

 some indifferent stage when no peculiar result would be expected, 

 for example, after gastrulation as it does in the bird with no 

 subsequent effect. In the light of the experimental production 

 of double individuals, it is readily understood that even though 

 the egg of the deer is interrupted in its development at an early 



