473 ON THE ZOOLOGICAL POSITION 



Prof. J. P. Hill, F.R.S. 



The Affinities of Tarslus from the Embryological Aspect, 

 (With Table, Plate I., and Text-figures 1-5.) 



My task in this discussion* is to consider what light the facts 

 of development throw on the question of the affinities of Tarslus. 

 ]n furtherance of that object, I have thought it might be both 

 useful and time-saving if I presented you Avith a brief summary, 

 in the form of the accompanying comparative table {v. p. 490), of 

 what I take to be the most important of the known facts relating 

 to the development, foetal membranes, and placentation of the 

 main groups of the Primates. For the purposes of this discussion, 

 I have set forth the facts relating to Tarsius in column 2 of the 

 table, in order that you may the more i-eadily compare them with 

 those appertaining on the one hand to the Lemuroids (Lemuri- 

 formes and Lorisiformes) in column 1, and on the other to the 

 Anthropoids in column 3. It remains to be seen in how far 

 this tripartite mode of grouping the Primates is justifiable on 

 embryological grounds. 



The first question which arises is that of the systematic position 

 and affinities of the Lemiu'oids. It is generally agreed that the 

 Lemuroids are a lowly and in many respects pi'imitive group, and 

 even Hubrecht admitted that they " ai'e in no respect a very 

 specialised order of Mammals." The prevailing view, widely 

 held both by comparative anatomists and palpeontologists, is that 

 they lie at the base of the Primate series ; but certain authorities, 

 notably Hubrecht, deny that they are in any way related to the 

 other Primates. That is a view which, on embryological grounds 

 alone, I am unable to accept. 



Unfortunately our knowledge of the development of the 

 Lemuroids is very fragmentarj^ but what we do know shows, 

 in my opinion, perfectly clearl}^ that the existing forms are 

 no such forlorn and degenerate creatures as some worild have us 

 believe, but, on the contrary, are to be regarded as the repre- 

 sentatives of a very old and primitive group of Mammals from 

 which the other and higher Primates may very well have taken 

 their origin. In their simple central type of development (the 

 blastocyst developing free in the uterine lumen), in their mode 

 of amnion formation (the amnion developing from folds in the 

 presence of a proamnion), and in the mode of development and 

 the relations genei-ally of their foetal membranes (in particular, 

 in the presence of a vesicular allantois, which grows out as a free 



* Since the date of the discussion, I have had the opportunity, thanks to the 

 great kindness of Dr. Dan. de Lange, Junr., Director of the International Institute 

 of Embryology at Utrecht, of examining a uterus of Tarsius, containing a nearly 

 full-term foetus with its placenta and of preparing sections of the latter. I wish 

 here to express my most cordial thanks to Dr. de Lange for his generosity in enabling 

 me to_ examine for myself this rare and valuable material. Its study has led to some 

 modification of the views I expressed at the meeting. 



