652 BERTHA E. MARTIN 



equal as to whether the dental lamina in front of the second tooth 

 will give rise to a tooth germ or degenerate. It is also conceiv- 

 able that this dental lamina might sometimes give rise to teeth 

 in front of the first tooth so that very hkely Leche did observe 

 fifteen tooth germs in a 46 mm. embryo; probably the first two 

 would not have developed far. Leche's Tatu peba may also 

 represent a different species from D. novemcinctus. 



As for homologizing these teeth with those of the adult animal, 

 there are present in all embryos in which teeth have reached any 

 degree of development, seven large teeth in the posterior part 

 of the jaw. They are distinguished from the other tooth germs 

 by their larger size, the above-mentioned posterior continuation 

 of the dental lamina beyond the last one of them, and the fact 

 that there exists a marked diastema between the first of these seven 

 teeth and the next tooth anterior to it. From their position in 

 the jaw, their shape and form, it is evident that these seven 

 teeth represent the seven functional teeth which are present in 

 the young skull, and posterior to the last of which the last func- 

 tional tooth is erupted five or six months after birth (compare 

 text figs. 2, 3, and 4). In front of the diastema, anterior to the 

 first of these functional back teeth, there occurs in the embyro 

 a tooth which during development becomes much larger than 

 the other front teeth, although it never attains the size of any 

 of the functional back teeth (text figs. 2, 3, and 4). In every 

 respect excepting size, this tooth outstrips all the other teeth in 

 its development. Thus it is the first tooth to acquire enamel 

 and dentine. Later in this paper, I have given a full description 

 of this tooth and will describe it here only as far as is necessary 

 in order to show the errors it has caused in previous interpreta- 

 tions of tooth homologies in Dasypus. See text figures 2, 3, 4 

 and 10, which show the relative, sizes of the different tooth germs 

 at various ages. At birth this tooth shows no evidence of de- 

 crease in its developmental activity and, a priori, there is no reason 

 for supposing that it will not become one of the functional back 

 teeth; in fact at birth it shows every evidence of being on the 

 verge of eruption, and moreover up to a later period of embyronic 

 development this tooth germ is not noticeably smaller than those 



