QUADRUPLETS IN NINE-BANDED ARMADILLO. 185 



In both cases the range of variation is five, or less than one 

 per cent. The difference in totals between the two sets is very 

 much greater a difference that does not indicate a sexual 

 dimorphism, for an examination of five unrelated specimens of 

 both sexes that happen to be on hand, shows a range of from 

 547 to 575 plates, a variation nearly six times as great as that 

 existing between a given set of quadruplets. 



This very marked similarity among the individuals of a given 

 set suggests that we have here a condition showing a degree of 

 identity that, in all probability, is at least as close as that found 

 in the well-known case of "true" or "identical twins" in the 

 human race, where it is supposed that each embryo arises from 

 from one of the two blastomeres of the two-cell stage. In the 

 case of Dasypns, each embryo probably arises from one of the 

 blastomeres of the four-cell stage. 



This immediately turns our attention to a further consideration 

 of the foetal membranes, the amnion and the chorion, and of the 

 manner in which they arise. It was stated above that each em- 

 bryo is enclosed in a separate amnion, and that the four amnia 

 are within a single chorion. We say single chorion advisedly, 

 because its surface gives no indication of being a multiple struc- 

 ture, that is, the product of the fusion of four chorionic vesicles 

 at an earlier period, as suggested by Lane; nor do the facts 

 revealed by a study of sections of the chorionic wall seem to bear 

 out such an interpretation. One must admit, however, the great 

 difficulty of any attempt at a correct interpretation of the exact 

 relationship existing between the foetal membranes as seen in 

 these advanced stages. The solution of that problem must be 

 sought in a study of young stages, when the membranes are in 

 process of formation. 



To have four ova ripen., be fertilized, and reach the uterus at 

 the same time, and always arrange themselves in a definite fashion 



or not these small plates would later have become separated off to form distinct ones, 

 but we are inclined to believe that such is the case, for in the adult armor there appear 

 to be no signs of double plates. If we count these rudimentary plates as complete 

 plates, then embryos I and 2 (Set A) would have exactly the same number of plates, 

 as would also embryos 3 and 4. The numbers of plates in the corresponding embryos 

 of Set B, although not identical, differ to the minimum extent, one plate in each 

 case. 



