AXD AFFINITIES OF TARSIUS. 495 



those previously esfcablisbed in connection with the skull and 

 teeth, the pla-centa and the digital formula of the hand, out- 

 weighed, in my opinion, the likeness between Tarsius and the 

 Lemurs, and enforced the removal of the former from the latter 

 and its association with the Monkeys, Apes, and Man in a group 

 of the Primates for which the term Haploi^hini was proposed, the 

 true Lemurs, the Lorises, and Chiromys being graded in contra- 

 distinction as Strepsirhini. The Haplorhini were divided into 

 two suborders, the Tai'sioidea for Tarsius and the Pithecoidea 

 for the Platyrhini (American Monkeys) and the Catai-hini (Old- 

 World Monkeys, Apes, and Man). 



This classification appeared, and still appears, to me to express 

 the known facts more accurately than its predecessors, the 

 nearest to it being that of Gadow who in 1898 definitely dis- 

 sociated Tarsius from the Lemurs, dividing the Pi-imates into 

 the three suborders Lemures, Tarsii, and Simije. Possibly he 

 Avould have anticij^ated my systematic arrangement had he been 

 acquainted with the structures connected with the muzzle and 

 vulva in Tarsius and other Primates and attached to them 

 the importance that I do. 



J. T. CuxxiXGHAM, M.A., F.Z.S. : — In the development of 

 Mammals generally segmentation of the ovum produces a small 

 internal mass of cells covered by a single layer of external cells. 

 Accumulation of watery liquid between these two parts produces 

 the blastocyst, a vesicle of epiblast cells with the inner cell-mass 

 adhering to the inner surface of the vesicle at one small area. The 

 wall of the vesicle is the trophoblast, which corresponds to the 

 epiblast layer of the serous membiane or false amnion of birds 

 a.nd reptiles. The next step in the mammal is the differentiation 

 of the hyjjoblast from the lower surface of the inner cell-mass : 

 this hypoblast grows round the inner siirface of the blastodermic 

 vesicle, and so forms the inner lining of the yolk-sac. The 

 amnion is formed either by coalescence of external folds above 

 the inner cell-mass or as a closed cavity within the latter. The 

 mesoderm is formed next by diflFerentiation between the epiblast 

 and hypoblast within the inner cell-mass, which may be now 

 called the embryo. The mesoblast extends between trophoblast 

 and hypoblast, and between trophoblast and amnion, splitting as 

 it goes to form a cavity called the extra-embryonic coelom. By 

 folding in of the sides of the embryo the connection of yolk- 

 sac and embryonic gut is narrowed, and from the hinder end 

 of the gut grows out the allantois as a hollow sac into the extra- 

 embryonic coelom. 



We have thus a membrane called the chorion, consisting of an 

 external layer of epibiast and an internal layer of mesoblast, 

 entirely enclosing the embryo with its three membranes, the 

 amnion surrounding it dorsally, and the yolk-sac and allantois 

 extending from the gut ventrally. These two sacs occupy varying 

 proportions of the inner surface of the chorion in different 



