596 THE OKGAN OP JACOBSON IN MARSUPIALS, 



tion complete, giving the cartilage the typical appearance on 

 section. 



The organ itself at its best developed part has on section a 

 moderately regular kidney shape, the hilus being directed almost 

 quite upwards and having in it a single large blood vessel. There 

 is extremely little glandular tissue in connection with the anterior 

 and middle part of the organ. The sensory layer is unusuall}'- well 

 developed, being aljout 3^ times as thick as the nasal epithelial 

 layer. The outer wall of the organ has small columnar cells only 

 about half the size of those of the nasal epithelium. 



Dasyurus macuhitus, Kerr, (adult). The organ in this species 

 differs considerably in a number of ways from tliat of D. 

 viven'inus. In almost all large animals the organ is less developed 

 proportionately, and appears to have less of a sensoi-y function, 

 and to become to a greater extent a glandular duct; and yet with 

 the difference in the character of the organ the cartilaginous 

 relations remain very constant in allied species and genera. The 

 onl}^ difference in the cartilaginous developments of the two 

 species of Dasyurus is a very slight one of degree; e.g., in D. 

 maculatus the cartilage is rather more developed in front, and 

 rather less posteriorly than in the smaller species. As regards 

 the organs, however, the differences are marked. The sensory 

 layer is present quite characteristically, but much less developed 

 than in D. viverrinus, while the whole organ is absolutely 

 smaller in lumen, which means that it is relatively only about 

 half the size. Instead of occupying almost the whole of the 

 cartilaginous hollow as in the smaller species, it fills only about 

 one-third the available space, the rest being almost quite filled up 

 by a great development of mucous gland tissue, except that 

 occujDied by the large hilar vessel. 



DIDELPHYID^. (Plate xlii.) 



In the American carnivorous genus Didelphys, we have a 

 number of points of close agreement with Dasyurus, and also a 

 few features suggesting a considerable gap between them. This 

 genus I have been able to study through the kindness of Sir. W. 



