58 aiJMMARY OF CURRENT RESEARCHES RELATING TO 



by the oculomotor nerve. In Tricho-nirus, and probably also in Phasco- 

 lomi/s, the primordium of the m. obliqnus inferior and the common 

 primordium of the mm. rectus inferior and rectus internus develop as 

 solid outgrowths from the posterior and ventral walls, whilst the 

 primordium of the m. rectus superior arises from the walls of a hollow 

 evaffination on the dorso-lateral side, the latter mode of origin resembling 

 that of all the oculomotor muscles in Lacerta. In Fhuscolarctos elongated 

 hollow outgrowths occur along the greater part of the posterior wall of 

 the cavity, an extensive budding here taking place. The further de- 

 velopment of these three muscles in the Marsupials agrees very closely 

 with that of the same muscles in Chebjdra. We cannot do more than 

 give a general indication of the scope of the paper. Attention may be 

 directed to the graphic plates drawn by E. A. Steele. 



Development of Heart in Marsupials.* — Katharine M. Parker has 

 studied this in Peramehs obesula. P. misnfa, Dasynrits virerrimis, and 

 Macropus riificoUis. The early stjiges are like those in Eutheria. While 

 the initiation of head-fold formation is in all probability due to the 

 forward growth of the brain-plate, there occurs also an active backward 

 growth of the anterior intestinal portal. This process is associated with 

 the rapid extension of the pericardium which occurs at this period of 

 development, and which brings about the backward and inward growth 

 of the layer of splanchnopleure limiting the pericardium. In the course 

 of this inward closure, the pericardial cavity extends to the ventro- 

 lateral, and finally to the ventral side of the lateral primordia of the 

 heart, so that when the lateral portions of the pericardium become 

 incorporated in its median liml). the heart primordia lie in the dorsal 

 wall of the pericardium. 



The approximation of the heart-tubes after gut-closure is due to the 

 fact that, at this period, the pericardium grows rapidly in length and 

 decreases in width, so that the heart-tubes are brought together by 

 longitudinal stretching t)f the pericardial wall lying between them. 

 Curvature of the heart is due to its rapid growth at a period of less 

 active extension of the pericardium. 



The first two aortic arches in Perameles are typical, and the develop- 

 ment of the veins of the head resembles that process in other mammals 

 in that the anterior cardinal vein is derived from persistent portions of 

 two primitive head-veins, the venas capitis medialis and lateralis. The 

 posterior continuation of the vena capitis medialis also contributes to 

 the formation of the posterior cardinal vein, and is itself derived from 

 the dorsal aorta. 



Placenta of Macacus.f — Ed. Retterer describes the structure of the 

 placental disks in 3Iacan(s rhesus. He finds that the foetal portion of 

 the placenta is due to the vegetative proliferation of the foetal chorion, 

 and that the maternal portion is due to the hypertrophy of the dermis 

 of tlie uterine mucosa. The common character of these two tissues of 

 different origin is the extensive retrogressive development which they 



* Proc. Zool. Soc, 1915, pp. 459-99 (2 pis. and 25 figs.), 

 t C.R. Soc. Biol. Paris, Ixxviii. (1915) pp. 323-7. 



