THE EVIDENCE OF THE OLFACTORY APPARATUS 



227 



As is seen, it is difficult to see any connection between these 

 folds of olfactory epithelium and the simple tube of the scorpion. 

 But in the nose, as in all other parts of the head-region of the 

 lamprey, remarkable changes take place at transformation, and 

 examination of the same tube in Ammococtes demonstrates that the 

 elaborate structure of the adult olfactory organ is actually derived 

 from a much simpler form of organ, represented in Fig. 99. Here, 

 in Ammoccetes, the section is no longer strikingly different from that 

 of the Thelyphonus organ, but, instead, most strikingly similar to it. 

 Thus, again, it is shown that this larval form of the lamprey gives 



■ cart 



Fig. 99. — Transverse Section through the Olfactory Passage op Ammoccetes. 



cart., nasal cartilage. 



more valuable information as to vertebrate ancestry than all the 

 rest of the vertebrates put together. 



Still, even now the similarity between the two organs is not 

 complete, for the tube in the lamprey opens on to the exterior on the 

 dorsal surface of the head, while in the scorpion tribe it is situated 

 ventrally, being the passage to the mouth and alimentary canal. In 

 accordance with this there is no sign of any opening on the dorsal 

 carapace of any of the extinct sea-scorpions or of the living land- 

 scorpions, such as is so universally found in the cephalaspids, trema- 

 taspids, and lampreys. Here is a discrepancy of an apparently 

 serious character, yet so wonderfully does the development of the 

 individual recapitulate the development of the race, that this very 

 discrepancy becomes converted into a triumphant vindication of the 



