IX. On the Systematic Position of Zeuglodon.* 
By Professor D’Arcy W. THompson. 
In another essay I hope to discuss fully, before long, the systematic position of the 
Cetacea. Those authors are, I am convinced, in the right, who from time to time 
have asserted the wholly anomalous position of this order among the Mammalia, and 
the impossibility of sustaining their derivation from either the Ungulates or the 
Carnivores in consonance with generally accepted views. To such a conclusion we 
are led, it seems to me, by almost every characteristic feature of the Cetacean 
anatomy: by the characters of the vertebrae, the carpus, the auditory ossicles, the 
larynx, the stomach, the mammary glands, the numerous phalanges, the numerous, 
similar, equi-distant, single-rooted teeth, the great development of the pterygoid in 
comparison with the palatine bones, and the simple and primitive characters of the 
placentation ; while the wide morphological differences present within the limits of 
the order, are in themselves no slight evidence of great antiquity. 
But however this may be, very obvious difficulties at once arise before us, in con- 
nection, namely, with the Zeuglodonts and the Squalodonts, both of which groups offer . 
numerous exceptions to the foregoing generalisations. The case of the Squalodonts 
is much the simpler of the two, though presenting certain special difficulties of its 
own; there can be, at least, no doubt as to their Cetacean nature. But as to the 
Zeuglodonts, which alone I propose to discuss here, it soon becomes manifest that if 
they be associated with the Cetacea, the problem of the origin of these latter 
becomes a thousand times more difficult: that then our definitions of the order 
become complicated by a crowd of exceptions, and that the theory of a primitive 
place for the Cetacea amongst the Mammalia falls to the ground. 
Briefly stated, my thesis in the present paper is simply this, that the Zeuglo- 
donts have no direct affinities with the Cetacea, but have, on the other hand, the 
closest possible relation with the Pinnipedes ; and, accordingly, that we may leave 
them out of account henceforth in our discussion of the classificatory position of the 
Cetacea. 
It is neither needful nor indeed possible to recount in detail here the innumer- 
able views that have been put forward regarding the affinities of these strange 
enormous animals. But it may be said that, since Owen first demonstrated that 
* The substance of this paper was communicated to the Congrés internationale de Zoologie in Paris in 
August, 1889, and is printed in the Compte-rendu of the Congress, under the title “ #aut-l associer les 
Zeuglodontes aux Cétacés ? 
