682 ON THE ORGAN OF JACOBSON IN THE ANT-BEAR. [June 15, 



structures taken some little distance behind fig. 6. It will be 

 seen that in lioth figures the organ is oval in section and that 

 the ciliated epithelium is found all round, the most specialised 

 portion being on the upper and inner sides. The greater part of 

 the cartilaginous groove is filled by a huge venous plexus quite 

 irregularly arranged. There is a fairly large artery, numerous 

 nerves and a little glandular tissue. On jjassing further back the 

 gland-tissue becomes much more abundant and the organ becomes 

 reduced to a narrow duct. Jacobson's cartilage near the posterior 

 end is reduced to a flat plate. 



In the relations of the organ perhaps the most sticking point is 

 the absence of any developments of the nasal-floor cai'tilage to 

 support the naso- palatine canal. Thus Orycterojms differs fi'om 

 all the Eutheria except the Edentata as exemplified by Dasypus, 

 and the aberrant Insectivore Macroscelides. Even from the pri- 

 mitive Ungulates such as Procavia or Sihs it difiers so greatly as 

 to suggest that any supposed Ungulate aflinities must be extremely 

 remote. 



The Rodents form, so far as the organ of Jacobson is concerned, 

 a group by themselves, but this group also must be very remote 

 from Orycteroj)us. We are thus forced to seek for the aflinities 

 among the more primitive mammals — the Edentates, Marsupials, 

 and Monotremes. 



Besides agreeing with these early mammals in the absence of 

 cartilaginous de\^elopments for the support of the naso-palatine 

 canal, it further agrees with them in having pi-esei'ved the outei- 

 cartilaginous bar which is probably the remains of the turbinal 

 of the organ. 



In the Edentata the organ has been described only in Dasypus 

 and a few notes have been made in the case of Manis. Dasypus 

 differs entirely fi'om Orycieropus in having the organ opening into 

 the nasal cavity and not into the naso-palatine canal and in many 

 other details. 2[anis agrees with Orycteropus in having a long 

 naso-palatine canal and in the organ opening into it, but in the 

 absence of figures or detailed description it is impossible at present 

 to say how far the agreement extends. 



On the Avhole the condition in Orycteropus comes nearest to that 

 in the Mai'supials, but there are many points of difference, of which 

 the most impoitant are (1) the absence of the papillary cartilage, 

 and (2) absence of a cartilaginous support to the lower glandidar 

 ridge. Less important are the shape of the organ, its mode of 

 opening into the naso-palatine canal, and the very irregular venous 

 plexus. In the structure of the nasal-floor cartilage there is some 

 resemblance to Echidna, but this latter has the organ and its 

 cartilages so much better developed that comparisons become 

 difiicult. 



The evidence from the study of this region would seem to point 

 to Orycteropus being descended from a line of ancestors the earlier 

 members of which Avere probably allied to Marsupials, whilst the 

 later members branched off from the Eutherian stem before any 



