494 The American Naturalist. [June, 
country, and are ready to join hands in pushing forward these 
investigations upon a joint basis. 
KUKENTHAL’S RESEARCHES. 
Kikenthal’s studies upon toothed whales were partly 
directed upon the theory of Weber, Julin and others that 
these animals were formerly heterodont. In the embryo of 
the Porpoise (Phocena communis,) he found traces of a 
heterodont condition quite sharply marked. There were 
twenty-five teeth in each half of the jaw, and the posterior 
seven were found to have two or three cusps. Having thus 
supported the opinion that the homodont toothed whales were 
primitively heterodont, Kiikenthal has also proved that they 
are diphyodont, and that the dentition of the toothed whales 
is a true milk dentition, while the second or permanent denti- 
tion is represented by rudiments which display a distinct 
crown of enamel and even the enamel pulp, yet does not 
reach the surface. i 
In the whalebone whales in which germs of teeth had been 
found in the first third of foetal life, Kükenthal does not con- 
firm the opinion of Weber that the dentition is heterodont. 
He denies that the posterior teeth are more complex than the 
nine anterior teeth, and holds that throughout they are simply 
conical, excepting in cases where two external teeth are fused 
together. This fusion of teeth does not follow any definite 
rule; in some cases it occurs in the anterior nine teeth. The 
course of embryonic development shows that these fused teeth 
represent an original condition, and in the opinion of the 
author, are to be regarded as molars. This conclusion was 
reached by the comparison of younger and older embryos, the 
number of fused teeth constantly diminishing in the latter. 
Kiikenthal advances the hypothesis that this was the method 
by which numerous homodont teeth arose from a small num- 
ber of heterodont, namely, by the splitting apart of cusps. 
This hypothesis he promises to support by paleontological a A 
evidence. He also shows that these embryonic teeth in the 
whalebone whales also represent the first or milk dentition; 
and that the rudiments of a second series of teeth develop — 4 
