FCETAL MEMBRANES OF CHIROMYS MADAGASCAKIENSIS. 1163 



In his speculations on the phylogeny of the placenta, Hubrecht 

 (10) starts out by denying a Reptilian origin for the Mammalia, 

 and postulates a primary phagocytic and absorptive activity on 

 the part of the trophoblast. From the very start of uterine 

 gestation, the trophoblast proliferating rapidly, invaded and 

 destroyed the maternal decidual tissue, and as the result, there 

 was formed a localised placenta of the '• deciduate " type in 

 which the maternal blood circulated either in endothelially lined 

 capillaries enclosed by trophoblast (Carnivora) or actually in 

 lacunar spaces in the ti-ophoblast itself (Insectivora, Rodents, 

 etc.). That being the pi-imary and original type of placentation, 

 it follows that all the "diffuse"' varieties of placenta in which 

 such phagocytic activity on the part of the trophoblast " was 

 insignificant or absent (Lemurs, certain Edentates, and many 

 Ungulates) " have been derived by simplification from the more 

 elaboi"ate "deciduate" type. Hubrecht admitted, however, that 

 " we cannot for the present indicate the intermediate steps by 

 which the simplification of a placenta of the Insectivorous 

 or Primate type dov/n to that of the present Lemurs was 

 brought about ..." (10, p. 115) ; but he saw " no reason why 

 this simplification should not have arisen more than once " 

 (p. 145) — i.e., the difiuse placentation of Lemurs" was not 

 necessarily obtained along the same hereditary line of develop- 

 ment'' as that of Ungulates. Indeed, he thinks there is sufficient 

 evidence to justify the drawing of a sharp line of distinction 

 between the placentation in these two groups. The late 

 Richard Assheton, in his critique of Hubrecht's monumental 

 paper (10), says (18, p. 268) : " 1 entirely agree with Hubrecht's 

 opinion that the diffuse placentation of the Lemurs is different 

 from that of the true plicate* forms of Ungulates, Cetacea, 

 some Edentates, etc." Further he v/rites (p. 265) : " Whether 

 the Carnivora or the extreme cumulative or extreme plicate 

 [placenta] is the most primitive, it is very difficult to say"; 

 nevertheless he goes on to suggest that the Lemurine placenta, 

 which he terms " pseudo-plicate," may possibly have been 

 derived by reduction from a cumulate type such as is found 

 in the Carnivora, " by way of such conditions as Eylohates, 

 Semnojyithecus, Oercocebus, by the gradual supersession of the 

 glandular activity of the maternal uterus over the phagocytic 

 activity of the foetal trophoblast, and the filling of the blood 

 spaces, into which the foetal villi originally hung, with uterine 

 secretions instead of extra.vasated maternal blood " (p. 269). 

 But why the Lemurs after having evolved a cumulate (deciduate) 

 placenta should have been under the necessity of substituting for 

 it the plicate (non-deciduate) type is not explained. 



* Assheton suggested a grouping of placental forms based on the behaviour o 

 the trophoblast into (a) Cumulate, characterised b3' radial, more or less loca 

 thickening of the trophoblast which is actively phagocytic (='' Deciduate")' 

 (b) Plicate, characterised by tangential extension and folding of the trophoblas' 

 with little or no phagocytic activity (= " Nondeciduate"). 



