BY K. jmooM. 615 



its whole extent. This peculiarity is well seen in the two species 

 of Dasyurus; in the small D. vlverrinus the glands are few, while 

 in the large D. niacn/aius they ai'e very numerous. I am not 

 iiware that sex has anj'thing to do with the peculiarities of this 

 remarkable organ, concerning the function of which we know so 

 little. 



In the three Polyprotodont genera the nasal-floor cartilage and 

 its inner division or -Jacobson's cartilage are very simple in 

 -structure and, as already pjinted out, bear considerable resem- 

 blance to the simple Monoti-eme type of Echidna. In Echidna, 

 however, the organ is much better developed, as is also the carti- 

 lage. By comparing the series of sections of the anterior region 

 of Jacobson's organ in Echidna, given in my paper on the organ 

 of Jacobson in the Monotremes, with the similar series from 

 Dasyurus (PI. xli.) there will be found no difficulty in tracing the 

 homology of the parts. In fig. 5 of the Echidna sections Jacob- 

 son's cartilage is found on section to be C-shaped, with the upper 

 outer end much thickened. By comparing this with PI. xli. tigs. 

 2, 8 and 11 from Dasyurus and Phascologale, it will Ije seen that 

 it is this thickened outer rim of the cartilage in Echidna that 

 becomes the outer bar of Jacobson's cartilage in Dasyurus. In 

 Echidna, on passing liackwards, the lower part of the C joins tlie 

 upper outer thickened bar (fig. 6), and a complete capsule is 

 formed; and on tracing the outer thickened bar still further back 

 it is found to be continuous with the turbinal plate, and represents 

 probably the rudiment of a turbinal which once extended right 

 to the front of the organ, as is still seen in Ornithorhynchus. In 

 Dasyurus and other Polyprotodonts the main differences are 

 due a.pparentlj'- to the feebler cartilaginous development. The 

 outer bar is present at- first in connection with the upper part of 

 Jacobson's cartilage as in Echidna, and almost immediately behind 

 the opening of the organ the lower border of Jacobson's cartilage 

 .sweeps round and becomes attached to it, bvit there is the difference 

 in Marsupials that as a rule before the lower connection is 

 established the upper has given way, so that there is usually for 

 a sh(^rt distance a fletached bar, which on section is apparently 



