PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. 101 
disappear, no new-formed follicles are produced, and the nutritive changes, in 
all probability, take place directly between the foetal and maternal blood. 
The amnion in the sloth is related to the chorion, placenta, and umbilical 
cord, as in the human female. The sac of the allantois and the urachus have 
disappeared, and I could see no trace of an umbilical vesicle. Further, I may 
state that the uterus is simple and uniparous, and that the mamme are two in 
number and pectoral in position. 
Tn classifying the Sloths and the other members of the Order Edentata it has 
been customary for zoologists to rank them with the lower orders of mammals. 
Professor Owen, for example,* directs attention to the supernumerary cervical 
vertebrze supporting false ribs, and the convolution of the windpipe in the 
thorax of Bradypus, as manifesting its affinity to the oviparous vertebrata, and 
to the unusual length of the dorsal and short tumbar spine in Cholepus as 
recalling a lacertine structure; whilst the abdominal testes, single cloacal 
outlet, low cerebral development, absence of medullary canals in the long bones 
in the sloths, and long-enduring irritability of the muscular fibre in both the 
Sloths and Ant-eaters, show the same tendency to an inferior type. In his 
system of classification, based on the cerebral characters, he places them in the 
group Lissencephala, along with the Rodentia, Insectivora, and Cheiroptera. 
Professor H. Mitne-Epwarps, in his most recent defence of his placental 
system of classification,t whilst admitting the insufficiency of the information on 
the mode of development of the Edentata, considers that, from the structure of 
the teeth and the absence of incisors, these animals have affinities with the 
Cetacea more than with other mammals, though they appear to have some 
relations with the Monotremata, and he does not hesitate to form a separate 
phalanx for their reception. Professor HaEckeEL, whilst ranking them amongst 
the Indeciduata,{ admits that the genealogy of the Edentata is very difficult. 
Perhaps, he says, they are nothing but a peculiarly-developed offshoot of the 
Ungulata, but perhaps their root may lie in a very different direction. 
The comparison which I have just made between the placenta of the sloth 
and that of the other deciduate mammals reveals a correspondence in impor- 
tant features, both of arrangement and structure, between the placenta of the 
sloth, that of the human female, and of the monkeys, greater than exists 
between it and the same organ in any of the other orders of the Deciduata, so 
far as has yet been described. This correspondence in placental form and 
structure between mammals, which on general zoological grounds are so widely 
* Reape Lecture “On the Classification of the Mammalia,” p. 31, 1869. 
t Considérations sur les affinités naturelles et la classification methodique des Mammiféres, being 
the first chapter in the Rechérches pour servir a l’histoire naturelle des Mammiféres, now in course of 
publication by himself and his son M. AnpHonse. Preface, dated 27th April, 1868. Paris. 
{ Natiirliche Schépfungs-Geschichte. Berlin, 1868, p. 480. 

