EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 111 
resumption of the facts as they present themselves to those 
who are unwilling to fall in with Strahl’s views, and because 
it allows us to group the other Insectivores and Rodents as 
far as known with the rabbit, whereas those carnivores, 
besides the dog, that have been carefully investigated up to 
now (cat, Putorius, fox) as well as most probably the bats 
(Fig. 140) all belong to the second category. Now if we 
remember the numerous points of comparison which the 
paleontologists have taught us to notice between early Car- 
nivora (as have been the Creodonts) and early Ungulates (as 
were the Condylarths), then we are induced to consider 
whether in respect to placentation the arrangements which 
on this head are characteristic for the living representatives 
of both orders! also merge into each other. 
A very strong argument in favour of the view here 
advocated is furnished by Assheton’s researches (’06) on the 
placentation of Hyrax (vide Fig. 145.) Here we have a 
mammal that in many respects offers archaic peculiarities, 
and that has been placed not far from the Rodents (Pro- 
caviidee !), from elephants, and from Ungulates by different 
1 Cretaceous tritubercular Creodonts are considered (vide Weber, 1904, 
p. 586) as having been parent forms, both of Condylarths and of other ungu- 
late families beside these, and I presume that it was during this process of 
evolution that the early placental arrangement underwent the simplification 
which so naturally leads from the arrangements as we know them for living 
Carnivores to those so-called diffuse placental, but in reality aplacental, 
arrangements of the Ungulates in general. 
Parallel phenomena of placental simplification occurred in two other great 
phyla of monodelphian mammals, most probably, however, at a yet much 
earlier period. This led up to the Lemurine so-called diffuse placenta on the 
one hand, to that of Manis (among Hdentates) on the other. Cetacea, 
Proboscidea, Sirenia equally seem to be examples of a placentation, which, 
like that of the Carnivora (resp. early Creodonts), finds itself on the road 
towards simplification. I presume there is great probability that in their 
ancestral forms all these orders more closely resembled the present Insecti- 
vores and Primates, as far as the complication of their placenta went, but that 
their considerable increase in size favoured extension with simplification of the 
placental area, as this is more evident yet in Ungulates and Lemurs. 
More details are given further on p. 144. 
