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 Ammoceetes 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 Ammoceetes, 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 
oe 
ope 
ERIN 
SOON 
sree 
e, 
GN 
2 
TeAee 
‘| 
By 
Bs 
5 
oh 
rags. 
Li je! - 
Sree 
‘Dr hid 
Fig. 99.—TRANSVERSE SECTION THROUGH THE OLFACTORY PassaGE OF AMMOCG@TES. 
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 
