718 SNOUT OF FCETUS OF MONOTREMES, 



originall}'^ described and figured by Professor W. K. Parker (4), 

 and again subsequently figured by Professor E. B. Poulton (5). 



To the gentlemen who have thus assisted me with valuable 

 material I desire to offer my grateful acknowledgments. 



The investigation has been carried on chiefly by means of serial 

 sections of the snout region. The sections were stained in hsema- 

 toxylin and picric acid. Wax-plate reconstructions were made 

 of the skeletal structures of the snout region of each of the 

 specimens, with the exception of C. The scale of magnification 

 employed for this purpose was 40 diameters. In the case of 

 Model i., (younger Ornithorhynchus) serial photographs of the 

 sections were traced directly, with thin manifolding carbon paper, 

 upon the surface of the wax-plates. In the case of the other two 

 models the drawings were made by tracing the image thrown on 

 the screen by the projection microscope, and then re-tracing with 

 the thin carbon paper directly upon the surface of the wax. 

 This has been found very convenient and greatly preferable to 

 the inclusion of the paper basis of the drawing in the wax-plate 

 according to Born's later method. 



For the figures illustrating this paper I am indebted to my 

 wife, as also for valuable assistance in the preparation of the 

 reconstructions. The figures representing the models have been 

 drawn from the models themselves, after photographs reduced to 

 a scale of about five-twelfths of the originals. The sectional 

 anatomy of the snout of the younger Ornithorhynchus is further 

 illustrated by the series of figures 13-21, which were drawn with 

 the aid of the Edinger's drawing-apparatus to a scale of enlarge- 

 ment of 18 diameters. 



I wish also to acknowledge the skilful assistance I have received 

 from my laboratory assistant Louis Schaeffer, both in the pre- 

 paration of the wax-plates and in photography of the models. 



I. — The cartilaginous rostral skeleton in the monotremes. 



In 1893 an important advance towards a more correct interpre- 

 tation of the cartilaginous skeleton of the anterior nasal region 



