Morphological Studies. 773 



the Ophidia and the Lacertilia^, are apart from it, endowed with a 

 very simple olfactory organ, — very simple as compared with the 

 nasal organ of Crocodilia and Chelonia. 



On the face of the facts, it looks as though these things stood in 

 relationship to each other. Possibly the nose-proper of Lacertilia and 

 Ophidia has a simple structure, because of the high development and 

 extreme delicacy, as a sense organ, of Jacobson's organ. On the 

 other hand the Crocodilia and Chelonia are recompensed for the 

 absence of Jacobson's organ by the much greater complexity of their 

 olfactory organs proper (vide nos. 43 and 16), 



GöTTE (10, p. 654), Fleischer (8, p. 8), Born (3, p. 120) and 

 KöLLiKER (20, p. 9) are inclined to regard the lower of the three 

 cul de sacs in the Anura as the homologue of Jacobson's organ. 

 This cannot be regarded as proved, or even as probable. The Lacer- 

 tilia and Ophidia appear to have no very close relationships with the 

 Anura, their Amphibian ancestors were probably of another type, 

 and the complexity of the nose in the Anura is explicable in the 

 same way as that of Crocodilia and Chelonia. 



It should not be forgotten that the parietal eye, a very old sense 

 organ found even in Cyclostome fishes and apparently in no others 

 (as a developed sense organ), is well developed in the Lacertilia, 

 while it is very highly degenerated in the Anura. 



In fact, these two organs alone, the parietal eye and Jacobson's 

 organ, appear to place a vast gulf between the Ophidia and Lacertilia 

 on the one hand, and the Anura on the other. They also sharply 

 separate the two groups of Reptiles 2) just mentioned from the Che- 

 lonia and Crocodilia. 



As WiEDERSHEiM remarks (54, p. 400) there appears to be no 

 homology between the so called Jacobson's organ of the Gymuophioua 

 and that organ of the Reptilia, and the so called Jacobson's organ 

 of the former group ought rather to be called the secondary olfactory 

 organ to prevent confusion. In no sense can it be rightly named a 



1) The Amphisbaenidae possess a Jacobson's organ whose structure 

 is completely Lacertilian. 



2) Prof, W. K. Parker (26, p. 407, No. 38, p. 636) concludes that 

 the skulls of snakes and Lizards present close resemblances in their 

 development. 



51* 



