376 VERTEBRATE ZOOLOGY 



mals, in that they depart consistently from the number seven, which 

 is so characteristic for mammals, having six, eight, or nine. They 

 are largely insectivorous in diet. Bradypus, the three-toed sloth, and 

 Chcelopus, the two-toed sloth, are the best known members of the 

 family. 



Sub-Order 2. Loricata (Armored Edentates; Armadillos). — The liv- 

 ing armadillos belong to the family Dasypodidoe and are much more 

 numerous in species than are the Pilosa. At least seven genera and 

 over twenty species have been distinguished. They are characterized 

 by having a well-developed dermal skeleton, composed of numerous 

 bony plates, in which hairs are imbedded, and which are covered with 

 horny scales. They have numerous teeth, which in the adult are 

 without enamel; but in the embryonic stages a well-defined enamel 

 layer has been discovered, which subsequently wears off. Incisors 

 are not found in the adult, but embryonic rudiments of these teeth 

 have been described. The armadillos range from moderately large 

 animals of three feet or more in length to small forms about the size 

 of a rat. Only a few of the species can receive mention here. The 

 little Chlamydophorus has a solid unjointed armature and is consid- 

 ered primitive in this respect. Euphractus sexdnctus (the Peludo) 

 is a decidedly hairy type. Tolypeutes has three movable bands and 

 rolls up into a ball. Priodontes is the giant among armadillos, being 

 three feet long to the base of the tail and having thirteen movable 

 bands in the armor. 



Dasypus novemcindus (the nine-banded armadillo) is the only 

 North American armadillo and therefore deserves especial attention. 

 It is really a South American species that has migrated northward 

 through Central America and now inhabits Mexico and Southern 

 Texas. It is a medium sized animal that lives in burrows in the day- 

 time and forages for insects at night. Its ears are long and close to- 

 gether and remind one of a donkey's ears. It is a source of satisfac- 

 tion to be able to contribute an adequate illustration (Fig. 193, C) 

 of this interesting species to take the place of the atrocious figure of 

 Flower and Lydekker, which was evidently drawn from a badly stuffed 

 specimen. Perhaps this armadillo deserves especial mention on ac- 

 count of its unique embryological features. It produces regularly, 

 with rare exceptions, four young at a birth, that are always all four 

 of the same sex. A study of the early developmental history of the 

 egg has revealed the fact that this is a case of specific polyembryony, 



