ON THE ORGAN OF JACOBSON. 157 



PAPERS. 



13. On the Organ of Jacobson and its Relations in the 

 " Insectivora." — Part I. Tupaia and Gymnura. By 

 R. Broom, D.Sc, M.D., C.M.Z.S. 



[Received March 9, 1915 : Read April 13, 1915.] 

 (Plates I. & II. *) 



Index. 



Structure: Page 



Tupaia : Organ of Jacobson 158 



Gymnura: „ „ 160 



In 1897, in " A Contribution to the Comparative Anatomy of 

 the Mammalian Organ of Jacobson," published in the Trans. Roy. 

 Soc. Edin., I called attention to the very great value of a study 

 of the morphology of the cartilages connected with Jacobson's 

 organ as a guide to the affinities of aberrant mammals. Changes 

 in habit bring about most marked alterations in teeth, bones, and 

 many viscera, but the delicate little cartilages in the nose are so 

 little affected that we find almost exactly the same type of 

 structure in forms so dissimilar as the sheep, cat, hedgehog, 

 bat, and lemur. And as the arrangement is an extremely com- 

 plicated one, we seem justified in concluding that the similarity 

 indicates affinity and common origin of those types rather than 

 independent developments of this remarkable structure. 



So far as at present known there are only two main types of 

 the organ of Jacobson and its relations found in mammals : (1) the 

 primitive or Marsupial type, which is a simplification of the type 

 found in the Monotremes, and which is retained with slight 

 modifications in such forms as Dasypus, Orycteropus, and the 

 Rodents ; and (2) the higher Eutherian type found in Ungu- 

 lates, Carnivores, Erinaceus, the bat Miniopterus, Lemur, and 

 Procavia. 



In 1902 I examined the organ in Macro scelides, hoping, in view 

 of Parker's discovery of mai'supial characters in the skulls of the 

 allied Pelrodromus and Rhynchocyon, that I might find some type 

 intermediate between that of the Marsupial and that of Erinaceus. 

 To my great surprise I found that in its relations the organ in 

 Macroscelides has no resemblance whatever to that of the typical 

 Insectivore, but agrees in practically every detail with the type 

 seen in the marsupial Perameles. 



In my paper " On the Organ of Jacobson in the Elephant 

 Shrew (Macroscelides proboscideus) " which appeared in the Proc. 

 Zool. Soc. 1902, vol. i. p. 224, I came to the conclusion that, 

 " from the fact that Macroscelides agrees with the Marsupials in 

 every detail of the anatomy of this region, we are forced to 

 the conclusion that it is a very near relative of the Marsupials, 



* For explanation of the Plates see p. 102. 



. Proc. Zool. Soc— 1915, No. XII. 12 



