No. 561] THE NINE-BANDED ARMADILLO 525 



poses, that of affording a critical demonstration of 

 parthenogenetic development of mammalian ova, and 

 that of furnishing a clue as to what we may expect to find 

 when we come to know the facts about the early cleavage 

 of normally developing eggs. In the latter connection it 

 is of interest to note that in Dasyurus, whose develop- 

 mental peculiarities up to the time of cleavage parallel 

 those of the armadillo, there is, as a preliminary to 

 cleavage, an elimination of the deutoplasmic material 

 almost precisely like that shown in our parthenogenetic 

 material. This fact lends support to the conjecture that, 

 in essential features, parthenogenetic cleavage parallels 

 that of normal development and may be used as a sub- 

 stitute for the latter, at least up to the eight-cell stage. 



For the sake of rendering the present account as 

 nearly complete as possible I shall make a statement 

 regarding the late cleavage and early embryology, based 

 partly on Patterson's observations. The earliest stage 

 shown by the latter at the Urbana meeting was an inner- 

 cell-mass stage, like that of any ordinary mammal. Such 

 a vesicle becomes attached by its animal pole to the very 

 apex of the fundus of the uterus, where it lies in a posi- 

 tion predetermined for it at a point where two grooves in 

 the uterine mucosa cross each other, the one running 

 laterally between the openings of the fallopian tubes and 

 the other at right angles from mid-dorsal to mid- ventral 

 aspects of the uterus. This position at the crossing of 

 these grooves enables the investigator to locate with cer- 

 tainty even the excessively minute earliest stages of the 

 developing vesicle. As it expands the vesicle becomes 

 depressed in the groove and elongates laterally into 

 ovoid form with the long axis running from the right to 

 left sides of the uterus. As soon as it gains attacl 

 to the uterine mucosa the vesicle undergoes germ-lay- 

 version like that seen in the rodents, the result being 

 two secondary vesicles are produced, an inner com~ 

 ectodermal vesicle and an outer endodermic vesicle, 

 complete at the area of attachment where the pri 



