NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 53 



Everyone who has had to do with counting the teeth of cetaceans 

 knows how variable the numbers may be. It is ahnost a miracle that 

 Kiikenthal should have been able to find five or six embryos, or 

 perhaps more, of Balcciwptcra muscidns, each of which had 53 teeth 

 or tooth cusps in the upper jaw (see Kiikenthal's more special account 

 in Jenaische Zeitschrift fiir Naturwissenschaft, vol. 26, 1892, p. 481, 

 together with his paper of 1893, /. c; in three other jaws the numbers 

 were less, a circumstance said to be accounted for by the fact that 

 some of the teeth had been resorbed). But even if it should prove 

 that B. luusculus always had 53 teeth in each jaw of the embryo this 

 fact would be without bearing on the question of the original denti- 

 tion in the whalebone whales. It will occur to nobody to regard 

 B. musculus as one of the most primitive species of the genus ; on the 

 contrary it is one of the highest, being one of the largest and most 

 elongated. Other species are found in the genus that stand on a 

 lower level ; this holds good especially of B. rostrata, and in this 

 species Eschricht has found the number of teeth in two embryos to 



be respectivelv ^ ± and ^^ (Unders. over Hvaldvrene, pt. 3, 1845, 

 40 40 ^ ' 



pp. 314 and 316-317). In two embryos of the same species Kiiken- 

 thal found 41 in the lower jaw (Jen. Zeitschr., 1892, pp. 485-486). 

 In two embryos of one of the highest species of the genus, B. gigas 

 (sibbaldii) Kiikenthal found 50 in the upper jaw (/. c, p. 486). In 

 several embryos of Megaptera hoops Eschricht has found from 46 

 to 51 teeth in each side of the upper jaw, and in the lower jaw rather 

 fewer, the least number 42 (/. c, pp. 311 and 316). Abel says, it is 

 true: " Bei jenen Bartenwalen, deren Kiefer eine geringere Zahl 

 als 53 Zahnindividuen aufweisen, handelt es sich entweder um fruhere 

 Embryonalstadien, wie bei dem von C. Julin beschriebenen Embryo 

 von Balsenoptera rostrata von etwa 48 cm. Lange (41 Zahne) , oder 

 um Reduktionserscheinungen " (/. c, p. 188) ; but this assumption is 

 entirely inadmissible. Abel himself probably had an inkling of it ; 

 he adds : " In dieser Frage miissten noch eingehendere Untersuch- 

 ungen auf breiterer Grundlage angestellt werden, um unsere bis- 

 herigen Kenntnisse in dieser Richtung zu erweitern." 



Neither can all of what Abel says about the number of teeth or 

 cusps in Patriocetus stand before a closer examination. It is not 

 certain that Patriocetus had 1 1 teeth in each jaw ; none of the skulls 

 that have been found has entire jaws, the anterior part is lacking in 

 them all. The number 11 is therefore only a guess, and scarcely 

 very likely ; judging from the rest of the cranial characters one would 



