

638 J. T. PATTERSON 



bud, either directly, through the formation of three secondary 

 buds from it, or through a further division of one of the two 

 secondary buds, after they had been formed in the normal way. 



It is to be regretted that the rare case of a two-embryo set, 

 referred to above, was not studied before birth occurred, as it 

 would doubtless have been found that the embryos occupied the 

 right and left sides of the chorionic vesicle, thus indicating that 

 each primary bud had been directly transformed into a single 

 individual. In that event, we should have had very strong evi- 

 dence in support of our contention that specific polyembryony in 

 the Dasypodidae began by the formation of a set of twins, per- 

 haps at first as sporadic cases of gemelliparous development such 

 as probably occurs in the production of duplicate twins in the 

 human species. 



However that may be, I have recently descovered certain evi- 

 dence in the early development of the Texas armadillo which 

 strongly supports this view concerning the origin of specific poly- 

 embryony in the Dasypodidae. It was pointed out in an earlier 

 section that when the secondary buds first appear, Nos. II and 

 IV apparently arise from the tips of the primary buds, as though 

 they were merely prolongations of these buds; while each of the 

 other secondary buds evidently arises slightly to one side of tip 

 of a primary bud. That is to say, that Embryo I always arises 

 to the left of its paired mate No. II, and likewise Embryo III to 

 the left of IV (fig. 2). This may be expressed in another way 

 by saying that buds I and III are outgrowths from the primary 

 buds, and that consequently they follow chronologically the 

 development of buds II and IV. The evidence upon which this 

 interpretation is based is to be seen in several of the young 

 blastocysts. 



It has been pointed out elsewhere that the first sign of a secon- 

 dary bud appears on the right side of the left-hand primary bud 

 in blastocyst No. 247 (fig. 1). The other embryonic bud is the 

 result of a prolongation of the extreme tip of the primary diver- 

 ticulum. In figures 2, 3, 4, and 28 is seen further evidence of 

 this same difference in the size of the two members of a pair of 

 embryos, and it is also evident in the sections (figs. 67, 77). 



