598 THE ORGAN OF JACOBSON IN MARSUPIALS, 



true Jacobson's duct, as it is lined with columnar epithelium. 

 The organ where best develoj)ed, as seen in fig. 3, almost com- 

 pletely fills the large hollow cartilage. On section it is kidney- 

 shaped, but the two poles are approximated so as to give the 

 organ an almost circular appearance, folding the small outer wall 

 closely on itself. The cartilage is supported by the small curved 

 palatine process at its lower and inner side. 



Didelpliys marsupialis, L., if)* (large mammary fo?tus, head 

 length 37 mm.). Between this form and the fcetal D. murina 

 there are a number of little differences, in addition to what can 

 be accounted for by difference of age. The nasal-floor cartilage 

 is nearly flat, and on passing backwards turns up at the base of 

 the septum as in D. murina. The inferior septal ridge is here 

 less developed, and the precurrent cartilaginous process, f)resent 

 in D. murina, is practically absent. In fig. 4 is shown a section 

 in the plane of the opening of the naso-palatine canal. Though 

 the papilla is well developed there is no trace of a papillary 

 cartilage, which is interesting as this is the only Marsupial I 

 have met with where it is quite absent. In fig. 5 the nasal-floor 

 cartilage is found divided and the premaxilla distinct from its 

 palatine process^ and in the space between the divided structures 

 is seen the anterior part of the almost vertical naso-palatine canal. 

 The outer part of the nasal-floor cartilage is still distinct. A few 

 sections behind this plane, as seen in fig. G, show the outer end 

 of the upper part of Jacobson's cartilage becoming detached, 

 forming the outer bar. The palatine process will be seen to bear 

 the same relation to the cartilage as in D. murina (fig. 2). In 

 fig. 7 the naso-palatine canal is seen opening into the nasal cavity, 

 as well as into Jacobson's organ. This last connection is effected 

 by means of a very short duct of Jacobson. In the next figure 

 the organ is closed from the canal which still connects the nasal 

 cavity with the mouth. 



* The species of this specimen was unknown, but there is veiy little 

 doubt that it is the young of the Common Opossum, DiilcJphyn mar.supialin, 

 L. 



