ORGAN OF JACOBSOlSr IN SPnEXODON. 419 



is probably still of the same type as that possessed by the 

 Cotylosauriaus. In the Squamata the organ has become greatly 

 developed and specialized, and more or less completely separated 

 off from the nose. 



The condition of Jacobson's organ in Sphenodon is of further 

 interest in that it affords additional evidence, if such be any 

 longer required, of the Reptilian alRnities of the Mammalia. 

 The palseontological evidence that Mammals are descended from 

 a primitive but true reptile seems to be pretty conclusive j but, 

 owing to most living reptiles having been much specialized, the 

 relations of the mammal to the reptile are not so striking when 

 one only studies the ordinary living types. In Sjphenodon we 

 have a reptile nearer to the primitive type than any other at 

 present alive, and it is thus particularly interesting to find in it 

 a type of Jacobson's organ so near to that of the mammal. In 

 tlie mamma], possibly as the result of the large development of 

 the incisor teeth, the organ has been forced to lie along the base 

 of the nasal septum, and while degenerating as a sense-organ it 

 has been retained largely as an excretory duct for the nasal 

 glands. 



Eepeeences to Literattjee. 



(1) W. Kitchen Parker. — On the Structure and Develop- 



ment of the Skull in the Lacertilia. Uoy. Soc. Proc. 

 xxviii. (1879) pp. 214-218 ; Phil. Trans. clxx.(1880) pp. 595- 

 640. 



(2) G. Born. — Die Nasenhohlen und der Tliranenausgang der 



amnioten Wirbelthiere. Morph. Jahrb., Bd. v. (1879) 

 pp. 62-140, & viii. (1883) pp. 188-232. 



(3) 0. Seydel. — Ueber Entwickelungsvorgange an der Nasen- 



hohle und am Mundhohleudache voq Echidna. Semon, 

 Zool. Forschungsreise, 1899. 



(4) Gr. Osawa. — Beitriige zur Anatomie der Hatteria punctata. 

 Arch. mikr. Anat., Bd. li. (1898) pp. 481-691. 



(5) Gr. B. Howes & H. H. Swinnerton. — On the Develop- 



ment of the Skeleton of the Tuatara, Sphenodon punctatus, 

 etc. Trans. Zool. Soc. xvi. i. (1901) pp. 1-86, pis. 1-6. 



