502 The American Naturalist. [June, 
midas. He anticipated from his studies upon the tooth 
development of the reptiles, that only traces of the dental fold 
would be found, and if any really rudimentary dentine teeth 
were found, they could only represent those primitive 
Selachian-like teeth which constitute the first series of the 
crocodile. In the crocodile as above noted, a first dental 
layer exhibits itself altogether similar to 
the placoid scales and the first teeth of the 
Selachians in the form of free papille upon the surface 
epithelium of the jaw. 
TAEKER’s RESEARCHES. 
Dr. Taeker of the Veterinary Institute of Dorpat, has com- 
pleted a most interesting series of studies upon the embryonic 
form of the teeth in the Ungulates. 
His technical methods were an improvement on those 
introduced by Klever, and his material included embryos of 
the horse as a type of the most complex form of perrissodactyl, 
of the pig as a modern bunodont, and of Selenodonts he 
selected the embryos of the Elk, Deer, Ox and Sheep, and of 
greater rarity, an embryo of one of the group of Tragulids. 
His conclusions are summed up as follows: : 
1. As a result of my investigations I find that both the Sui- 
dæ with rounded or bunodont cusps, and the Ruminants with 
their crescentic or selenodont cusps, arise from a similar initial 
bunodont stage; that is,-all the highly complex forms of 
modern cusps spring from the simple ancestral hillock in 
the embryonic stages. 
« 2. The order of differentiation soon follows, in which the 
Separate cones and conids (cusps of the lower jaw) are trans- 
formed into pyramids in the case of the pig, and into cres- 
cents in the case of the ruminants. 
3. The transformation of the cones is not effected simultan- 
eously, but successively. In the upper teeth it does not begin 
with the ‘protocone (antero-internal cusp which is first 
developed in the paleontological history), but with the 
external cusps, the paracone and metacone. 
