648 BERTHA E. MARTIN 



sufficiently complete to enable them to work out the full history 

 of tooth development, and they were obliged to draw their con- 

 clusions from a few isolated stages. 



Through the kindness of Professor Newman in giving me 

 access to his large collection of embryos of Dasypus novemcinctus, 

 I have been able to choose a series of stages which gives a com- 

 plete history of events from the time of the laying down of the 

 dental lamina until birth. I have examined the following em- 

 bryological stages: 30 mm., 35 mm., 48 mm., 50 mm., 53 mm., 

 55 mm., 61 mm., 65 mm., 71 mm., 75 mm., 78 mm., 82 mm., 

 83 mm., 92 mm., 100 mm., 103 mm., and 108 mm. These 

 figures give approximately only the relation of these stages to 

 each other, for two stages showing little difference in size, may 

 show a great difference in degree of tooth development; and on 

 the other hand, two stages differing much in size may show little 

 difference in that respect. That degree of development is not 

 always associated with size may be seen from the fact that the 

 100 and the 108 mm. foetuses were full term. My stages repre- 

 sent a complete series in tooth development, and there are no 

 wide gaps. Unfortunately the picture after birth is not com- 

 plete, as I was not able to procure any stages between that of 

 the foetus at full term, and post embryonic stages of at least 

 four months after birth. It is impossible to breed these animals 

 in captivity as the mother devours her young as soon as they are 

 born, and the young cannot be reared by hand. In the wild, as 

 soon as the young are born, the mother retires with them to almost 

 inaccessible places in the rocks, and does not bring them out 

 until they are several months old. Mr. Johns, of the Armadillo 

 Curio Company in Boerne, Texas, tried in vain to get some of 

 these young animals for me. Through this same collector, I 

 have succeeded in obtaining a large number of young animals 

 several months old (probably 4 to 6). However, these skulls 

 have proved of little value except for gross observations, being 

 very unsatisfactory for histological study. During the journey 

 from Texas, the containers had broken, and most of the formalin 

 in which the animals were fixed had leaked away. Moreover 

 it was almost impossible to decalcify the jaws sufficiently for 



