102 ON THE PLACENTAL STRUCTURES OF THE TENREC 



any of their structures, either interfered with or superposed upon 

 them ; and for the entire class the term ' non-deciduate ' is pro- 

 posed by Professor Huxley. The first question which arises is : 

 What number of general propositions can we make as to the 

 entirety of this class, to a certain similarity existing between the 

 least mutually resembling members of which testimony is borne 

 by the trivial names of ' sea-cow' and 'sea-camel' as applied to 

 certain of the herbivorous, and ' Meerschwein ' to certain of the 

 carnivorous Cetacea ? There is a considerable number of such 

 propositions ; but it is not always easy to say whether certain of 

 them are not correlated, either in the way of nutrition with the 

 large size which distinguishes this division of placenta as a whole, 

 or in the way of function with their peculiar modes of life, and 

 are therefore of little classificatory value. It is as functional 

 correlations perhaps, that we should note the absence of clavicles 

 and the faculty of self-help which the young of all non-deciduate 

 mammals possess from their first entrance into the world ; and 

 I should incline to consider as a correlation of growth the posses- 

 sion of complexly convoluted brains by these animals, since in the 

 class to which they and their deciduate allies both belong, the 

 complexity of the convolutions varies very commonly in a direct 

 ratio with the increase of bulk. Neither of these explanations, 

 however, will account for the fact that in all the non-deciduate 

 Mammalia we find one superior cava, and one only, and that in the 

 whole class, so few of the members of which are multiparous, the 

 uterus still retains a bifid character, its cornua greatly predomi- 

 nating over the corpus uteri. In antithesis to the deciduate 

 mammals, we find in the non-deciduate a general, though not a 

 universal co-existence of comparatively simple livers and simple 

 lungs with complex stomachs. I am not aware that anal glands 

 have been observed in any non-deciduate mammal. It is well 

 known that the generative organs of both sexes in the Artiodactyles 

 and the Cetacea proper are ' almost exactly similar 1 ,' only that the 

 testicles are not external, and there are no external parts in the 

 females of the latter order. 



The great abundance of blood and the great relative abundance 

 of blood-cells are points common to the pig and to the porpoise ; and 



1 Hunter's ' Essays and Observations,' ed. Owen, vol. ii. p. 105 ; and ' Hunterian 

 Catalogue,' vol. iv. 2527. 



