486 ON THE ZOOLOGICAL POSITION 



where it apparently persists as a solid strand, connecting the 

 embiyonal formation directly with the chorion (text-fig. 5, est.). 

 Even if this strand is reinforced later by mesoderm of primitive 

 strea,k origin, it is clear, if th« connecting stalk arises in the way 

 outlined, that it is more crenogenetically modified than is that of 

 Tarsias, the latter providing the link between the Lemuroids and 

 the Anthropoids. 



In both Tarsius and the Anthropoids, the connecting stalk 

 later on becomes enclosed with the yolk-stalk in a tubular 

 prolongation of the margin of the umbilical opening, which 

 carries the amnion with it. The cord-like structure so formed is 

 the umbilical cord, which connects the embiyo with the placenta. 

 In examining the foetal Tarsius which Dr. de Lange so kindly 

 sent me, I noticed that the cord is related to the placenta some- 

 what differently to that of the Anthropoids. Whereas in the 

 latter, the cord takes the form of an elongated, more or less 

 twisted, rope-like structure which runs as a free cord to become 

 connected with the chorion covering the free surface of the 

 placenta, usually near its centre, in Tarsius the cord is quite 

 short, and instead of passing directly to the placenta, it joins the 

 chorion soon after it becomes clear of the body of the ftetus and 

 runs down in that to join the distal margin of the placenta 

 (text-fig. 1). This difference confirms the conclusion we reached 

 above that the development of the cord does not follow identical 

 lines in the two groups. 



Lafjtly, let iis see what conclusions as to the affinities of Tarsius 

 may be drawn from the study of the placenta itself. The 

 development and structure of this remarkable organ were de- 

 scribed by Hubrecht in a lengthy paper published in 1899, but in 

 that pa,per Hubrecht was more concerned with demonstrating the 

 occurrence of a supposed blood-forming or ha?mopoietic process 

 in the placenta than with the description of the structure of the 

 ripe organ itself, and his figures fail to convey an adequate idea 

 of its characteristic structural features. That defect I have 

 attempted to remedy by the provision of the microphotographs 

 of sections of the nearly 'full-term placenta shown m fig. 1, and 

 herewith reproduced as figs. 2, 3, and 4, PI. I. 



These figures supplement Hubrecht's account of the placenta 

 very materially, and illustrate quite adequately, I think, the more 

 important features in its structure. Erom these figures, anyone 

 who is familiar with the sectional appearance of the human 

 placenta, will recognise at once that he is dealing with a placenta 

 of the Anthropoid type. Hubrecht, Avith reference to his own 

 <ig. 66, remarks "eine entfernte Aehnlichkeit mit der mensch- 

 Uchen Placenta, wie sie Sedgwick Minot abbildet, ist nicht 

 zu verkennen," and that is certainly the conclusion that any 

 competent embryologist would come to from an inspection of 

 my fig. 4. The general resemblance is indeed extraordinarily 

 striking, but, whilst tb.at is so, it must be emphasized that in its 

 detailed structure, the Tarsius placenta shows peculiarities of its 



