ZOOLOGY. 299 



now satisfactorily proved, however, that no decidua is de- 

 veloped, and the placenta exhibits a modification of a zonary 

 form. " Both in form and structure," says Mr. Turner, " the 

 placenta in the lemurs is without doubt a diffused placenta." 

 The question naturally arises, What is the value of the 

 placental characteristics of the Prosimians? Are those ani- 

 mals related most to the other forms developing a decidua, 

 or to the Primates, with which they have been hitherto gen- 

 erally associated, or at least approximated to? Professor 

 Turner has quite judiciously treated this question; and has 

 contended that in spite of the placental characters, the Pro- 

 simians are closely related to the typical or ape-like Primates, 

 with which thev a^ree, or most resemble in a number of 

 osteological and cerebral characters. He urges, however, that 

 the two groups are entitled to ordinal value; the apes, with 

 man, belonging to one (Primates), and the lemurs and related 

 types to the other (Prosimians). He urges, with consider- 

 able force, that the non-deciduate " diffused placenta has the 

 most simple mode of structure, and that the distribution of 

 the villi over the surface of the chorion presents a closer ap- 

 proximation to the primary embryonic arrangement ; while 

 the discoid placenta exhibits the greatest departure from the 

 diffused villous chorion of the early embryo." It is there- 

 fore probable, he thinks, that the mammals with discoid de- 

 ciduate placenta have diverged from those characterized by 

 a non-deciduate one. He has shown, too, that the line of 

 demarcation between the non-deciduate and deciduate pla- 

 centiferous mammals is not so abrupt as has usually been 

 supposed, but is graded over by an intermediate arrange- 

 ment " the passage from the diffused placenta, in which no 

 maternal tissue decid nates during parturition, to those de- 

 ciduate placenta3 in which both the epithelial and subepi- 

 thelial vascular tissue of the uterine mucosa are shed being 

 effected through the cotyledonary placenta, in which the 

 epithelial lining of the maternal cotyledons separates along 

 with the foetal villi." There is, besides, considerable varia- 

 tion in the relative proportions of the tissues. 



