SECTIONAL TRANSACTIONS.— D. 337 



type of temporaril}- attached ectoplacenta seems to me the starting-point of the other 

 placental forms. In large animals with spacious uteri and a large production of 

 glandular secretion the attachment is delayed (C'arnivora) or does not occur at all 

 (most Ungulates). The placenta oi Manis is completely h»mochorial ; still, I have 

 found some traces of a former attachment, i.e. two vestigial placental cushions. 

 Opposite one of these, an ephemeral plasmodiblast develops. Thus, there is a slight 

 indication of a former more intense interaction between maternal wall and 

 trophoblast. In the endotheliochorial placenta, the border haematome of the 

 placental girdle may be considered as a derivate of the primitive ectoplacenta, while 

 next to it develops a placental labyrinth bj^ the intermingling of maternal and foetal 

 capillaries. The maternal capillary system is first to develop and determines the 

 pattern of the labyrinth. In Orycteropus a very low type of endothelial placenta 

 occurs, which lacks a real labyrinth, because the foetal capillary sj^stem only shows a 

 slight development. On the other hand, the border haemotomes are strongly developed 

 as is the trophoblast at the same spot. In the Bradipodidae the placenta does not 

 possess the girdle-form, and extensive hEemotomes are lacking. On the contrary, 

 there is the beginning of labyrinth-formation and the maternal capillaries show a 

 tendency to lose their endothelial wall. This leads to the conditions in Chiroptera, 

 where a haemochorial, labyrinthiform placenta is formed by the brealdng down of the 

 maternal endothelium in a younger typically endotheliochorial stage. In the case of 

 Miniopterus the two stages are found in the ripe placenta. In the olliform placenta, 

 on the other hand, the stage of an endotheliochorial labyrinth is never passed. The 

 lacunae of the ectoplacenta are filled with maternal blood but they have never been 

 maternal vessels. The confluence of these spaces gives rise to the intervillous space. 

 The placental development of Galeopithecus characterised by the lack of a connective 

 stalk and by the large extent of the allantois is an example of the formation of an 

 olliform placenta in a way independent from that of the Primates. The olliform 

 placenta of the Dasipodidse deviates in a still more obvious manner from that of the 

 Primates. Here the foetal trophoblastic villi corrode large spaces in the maternal 

 stroma, but the roofs of these spaces and the uterine epithelium of these roofs remain 

 intact. So intervillous spaces are formed bordered on all sides by maternal con- 

 nective tissue and not by a trophoblast layer. ' 



Finally, most Rodents and Insectivores show a labyrinthiform, haemochorial 

 placenta with important remains of ectoplacental tissue. Here the haemochorial 

 condition arises partly by the transformation of the ectoplacenta, partly by the 

 changing of a previous endotheliochorial stage. Thus, there are at least four types 

 of haemochorial placenta which have probably arisen quite independently from a more 

 primitive attached, histiotrophic stage. I think these examples are sufficient to make 

 it probable that each of Grosser's placental types has a polyphyltic origin. 



Dr. C. Tate Regan, F.R.S. — The Evolution of the Primates. 



Five sub-orders of the Primates are recognised, the relationship of which may be 

 expressed diagrammatically thus : — 



Tarsioidea Platyrrhina Catarrhina 



Lorisoidea 



1 

 Lemuroidea 



The resemblances between the Platyrrhines (American Monkeys) and the Catar- 

 rhines (Old World Monkeys, Apes and Man) are due to parallel evolution. Tarsius 

 is remote from the ancestral line of man, whose nearest living relativeis the Chimpanzee 

 but whose ancestor probably did not belong to the same family as this ape. 



Prof. F. H. Edgeworth. — On the Musculature for opening and closing the 

 Mouth in Vertebrates. ' 



The jaws are raised and the mouth shut by the masticatory muscles in all Verte- 

 brates. They are depressed and the mouth opened by various groups of muscles. 



1930 Z 



