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Dr. M. Watson. 



characteristics not hitherto met with in the placenta of any other 

 mammal. And yet, to associate the members of either of these groups 

 would, taking into consideration the wide divergence which they 

 otherwise structurally possess, be as rational as to group together the 

 elephant and the spotted hyaena, simply on account of the possession 

 by the' female of both of these animals of a urogenital canal, pre- 

 senting peculiar features not met with in that of any other mammal. 

 A natural classification cannot possibly be based upon the form or 

 structure : of any one organ in any group of animals, but must take 

 into consideration the various modifications of every organ of the 

 animal body ; and more especially of those proved by research to be 

 of great morphological, although not necessarily of equal physiological, 

 significance. As additional evidence of the slight value to be attached 

 to the form or structure of temporary uterine -and foetal structures as 

 affording a basis of classification, I may refer to the fact 'that whilst the 

 structure of Procyon is such that it has very properly led naturalists to 

 associate that genus with the arctoid group of Carnivores, yet the foetus 

 ef Procyon lotor is provided with a supernumerary cuticular invest- 

 ment, or epitrichium, of which, according f to the observations of 

 Welcker,* the foetus of TJrsus presents not a trace. Of the structure 

 of the bear's placenta we at present know nothing, but when it comes 

 to be examined, in view of the inconstancy of foetal structures in the 

 members of one and the same group of mammals, there seems to be 

 little ground to anticipate that vessels presenting the peculiarities 

 above described in the placenta of Procyon, will be found to be any 

 more characteristic of the arctoid group, as a whole, than the epitri- 

 chium has proved to be. 



The foetal membranes of 'Procyon agree for the most part with 

 those of other Carnivora. The absence, however, in the former of an 

 umbilical vesicle in the advanced condition of the embryo, is remark- 

 able, and appears 1 to separate Procyon from every other member of the 

 carnivorous group of mammals. The chorion differs in no respect 

 from that of other Carnivora. In Procyon, as in Canis, Felis, and 

 PJioca, the placental vessels extend beyond the placental into the non- 

 placental area of this membrane. The allantois presents a similar 

 arrangement in all Carnivora. With regard to the amnion, Procyon 

 agrees with the members of the plantigrade section of Carnivora at 

 the same time that it differs from those of the digitigrade and 

 pinniped sections in the late closure of the amniotic sac, in the close 

 attachment of that sac at one spot to the foetal surface of the placenta, 

 and (adopting Bischoff's view)f in the consequent deficiency of 

 placental substance at that spot. 



* " Abhand. der Naturf. Oesellsch ," Halle, Band ix, p. 39. 

 f " Si:zungsber. der Akad. Wissensch.," Muncken, 1865, p. 219. 



