On the Female Organs and Placentation of the Racoon, 295 



maternal vessels of Cholcepus. I have already referred to the difficulty 

 of reconciling two sets of observations, in accordance with one of 

 which, these vessels appertain exclusively to the foetus (Procyon), 

 whilst according to the other they belong as exclusively to the mother 

 {Cholcepus). This difficulty must remain until the placenta of Procyon 

 has been re-examined after successful injection of both the foetal and 

 maternal vessels. But, even granting that future research may allot 

 the colossal capillary system of Procyon to the mother and the ordinary 

 capillary system of its placenta to the foetus, the mere presence of 

 vessels of so peculiar and identical character in the placentas of Pro- 

 cyon lotor and Cholcepus Hoffimanni — animals between which there is 

 not a single additional point of structural resemblance, — and the 

 absence of such from the placenta of every other Carnivore which has 

 hitherto been accurately examined, appears to me to afford only one 

 additional proof to the many hitherto adduced of the futility of any 

 attempt to base a sound classification of the Mammalia upon the form 

 and structure of the placenta. There does not, indeed, appear to be any 

 reason why the placenta, either in respect of form, structure, or both, 

 should agree in animals which are closely allied, or differ in species, 

 which upon other grounds we regard as widely separated from one an- 

 other. The researches of Turner and others have made us aware that, 

 reduced to its essentials, the connexion between the mother and the 

 child is the same in all mammals, that is, it consists of an intimate con- 

 tact of the foetal and maternal blood-vessels. This, however, is simply a 

 physiological necessity, the accomplishment of which may be brought 

 about in many different ways. A priori, therefore, the particular 

 arrangement by means of which this is accomplished is hardly likely 

 to be constant in, or confined to one group of mammals, or such as will 

 result in the formation of an organ which structurally, or morpho- 

 logically, is likely to be of any value in affording a basis of classifica- 

 tion. The zonary form of placenta is met with in such widely 

 separated groups as the Carnivora, Hyracoidea, and Proboscidea, 

 whilst the diffused placenta is common to the Suidse, Delphinidae, and 

 Equidae, and any classification based upon the possession by forms (in 

 other respects so widely separate) of a single organ, the placenta, 

 simply because it possesses the same form in all, must necessarily lead 

 to error in classification, if by classification we understand the group- 

 ing together of animals in accordance with their affinities, that is, 

 in accordance with their entire structural organisation. Similarly, to 

 attempt to classify the Mammalia in accordance with the structure 

 of the placenta would lead to the association of forms which in other 

 respects have nothing in common. The Suidae and Lemurina, in 

 respect of the structure and arrangement of the vessels composing 

 this organ closely resemble one another, as do also Procyon and 

 Cholospus in the possession of vessels which present structural 



VOL. XXXII. X 



