168 Charles Searing Mead. 



The Siis embryo studied was 30 mm, long (head-rump measure- 

 ment), and the lenglli of its head 12 mm. The head was cut trans- 

 versely into 795 sections, each 0.015 mm. thick. The cartilage in 

 all the even-numbered sections was drawn with the aid of a projec- 

 tion apparatus, the drawings being enlargements of 25 diameters. 

 In making the reconstruction, Bern's wax plate method was used. 



For comparison I have had Ziegler's wax models of the chondro- 

 crania of man, Gallus, Lacerta and Rana. In addition, Professor 

 Eugen Fischer, of the University of Freiburg, loaned me his re- 

 constructions of the Semnopithecus, Macacus, Tarsius and Talpa 

 skulls, and the series of sections from which his Talpa reconstruction 

 was made. Also a reconstruction of the primordial cranium of Lepus, 

 prepared by Dr. Max Voit, has been of service. 



Of the models and reconstructions used for comparison, the one 

 of Talpa resembled more closely that of Sus than did any of the 

 others, and, hence, has been referred to most frequently in the com- 

 parisons. 



The literature dealing with the development of the mammalian 

 skull is very extensive. The publications of Parker, Spoudli, 

 Kolliker and Decker, on the chondrocrania of the mammals, are the 

 principal works belonging to the old school, in vdiich the skulls were 

 prepared principally by the maceration method. The introduction 

 of Bom's wax plate method of reconstruction has made possible 

 not only a more exact study of the embryonic cranium itself, but 

 has also enabled one to study the surrounding tissues as well. A 

 more fundamental view of the skull is thus obtained. Among the 

 more recent papers on the embryonic skull may be mentioned Gaupp's 

 "Die Entwickelung des Kopfskelettes" in Hertwig's Handbuch 

 (1905b), valuable on account of its general survey; also his ex- 

 tensive contribution on the development of the skull of Echidna 

 (1908). The papers of Fischer on Talpa (1901 b) and the apes 

 (1903) and a forthcoming paper of Voit on Lepus (1909) likewise 

 contain valuable results. 



This investigation was undertaken at the suggestion of Professor 

 Ernst Gaupp. The work was conducted. in the laboratory of the 

 Comparative Anatomical Institute of Freiburg in Baden. 



