162 



ON THE ORGAN OF JACOBSON. 



those in Tupaia, it will be seen that the two differ so greatly in 

 type that it is a little difficult to homologise some of the 

 structures. "While Tupaia agrees closely with the Marsupial 

 type, Gymnura agrees equally well with the type found in most 

 Eutherians. In my paper of 1897 I suggested the division of 

 the Eutherians into two superorders — the Coenorhinata to include 

 those orders with the higher type of nose structure, and the 

 Archseorhinata for those with the primitive type. 



In the Coenorhinata I placed the Carnivora. Insectivora, 

 Artiodactyla, Perissodactyla, Chiroptera, Primates, with probably 

 the Sirenia and Cetacea. "We now know that the Hyracoiclea 

 also belong to this superorder. In the Archseorhinata were 

 placed the Edentata and Rodentia. 



Gymnura has the structures connected with Jacobson's organ 

 almost exactly as in Erinaceus, as we should have expected, and 

 very similar to those in Felis. 



Tupaia and Macroscelicles have the nasal structures formed, as 

 in the Polyprotodont marsupials, on an entirely different type, 

 and there can be no doubt whatever that they have no near 

 relations with such types as Erinaceus and Gymnura and must be 

 removed from them and placed in a distinct order, Menotyphla. 



In Part II., which will deal with the structures in Oentefes, 

 Ckrysochloris, and Talpa, will be discussed at greater length the 

 relationships of the different groups. 



EXPLANATION OF THE PLATES. 



Lettering. 



a.r.c, anterior recurrent cartilage; I.t., inferior tnrbina] ; J.c, Jacobson's 

 cartilage; J.o. Jacobson's organ; l.d., lacrymal duct ; Mx,, maxilla; Na., nasal ; 

 n.g.d., nasal-gland duct ; n.p.c, naso-palatine canal ; n.s., nasal septum ; o.b.J.o., 

 outer bar of Jacobson's organ ; p.c, papillary cartilage ; Tmx., premaxilla ; p.n.f.c, 

 posterior nasal-floor cartilage; p.Pmx., palatine process of premaxillary ; Vo., 

 vomer. 



PiATE I. 



Fig. 1. Section through snout of Tupaia sp. across anterior part of premaxilla. 

 Figs. 2-6. Sections across the snout of Tupaia sp., through different regions of the 



palatine papilla. 

 Fig, 7. Section through the organ of Jacobson in Tupaia sp. a short distance behind 



the papilla. 

 Fig. 8. Section through the organ of Jacobson in Tupaia sp. towards the posterior 



part of the organ. 



Plate II. 



Figs. 9 & 10. Sections across the nose of Gymnura a short distance in front of the 



premaxilla. 

 Fig. 11. Section across the snout of Gymnura in the region of the anterior part of 



the premaxilla. 

 Figs. 12 & 13. Sections across the snout of Gymnura in the region of the palatine 



papilla. 

 Fig. 14. Section across the snout of Gymnura immediately behind the papilla. 

 Fig. 15. Section across the organ of Jacobson in Gymnura behind the anterior 



palatine foramen. 

 Fig. 16, Section across the posterior part of the organ of Jacobson in Gymnura. 

 All figures are 12 times enlarged. 



