THE EVIDENCE OF THE OLFACTORY APPARATUS 221 
situated, independent appendages. Still, even here there is the strik- 
ing fact that the nerves of these olfactory organs always arise from 
the supra-cesophageal ganglia, although those to the second pair of 
antenne arise from the infra-cesophageal ganglia, just as the olfactory 
nerves of the vertebrate arise from the supra-infundibular brain-mass. 
Not only is there this similarity of position, but also a similarity of 
structure in the olfactive lobes of the brain itself of so striking a cha- 
racter as to cause Bellonci to sum up his investigations as follows :— 
“The structure and connections of the olfactive lobes present the 
same fundamental plan in the higher arthropods and in the verte- 
brates. In the one, as in the other, the olfactory fibres form, with 
the connecting fibres of the olfactory lobes, a fine meshwork, which, 
consisting as it does of separate groups, may each one be called an 
olfactory glomerulus.” 
He attributes this remarkable. resemblance to a physiological 
necessity that similarity of function necessitates similarity of structure, 
for he considers it out of the question to suppose any near relationship 
between arthropods and vertebrates. 
Truly an interesting remark, with the one fallacy that relationship 
is out of the question. 
The evidence so far has consistently pointed to some member of the 
paleostracan group as the ancestor of the vertebrates—a group which 
had affinities both to the crustaceans and the arachnids ; indeed, many 
of its members resembled scorpions much more than they resemble 
crustaceans, The olfactory organs of the scorpions and their allies are, 
therefore, more likely than any others to give a clue to the position of 
the desired olfactory organs. In these animals and their allies paired 
olfactory antenne are not present, either in the living land-forms or 
the extinct sea-scorpions, for all the antennz-like, frequently chelate, 
appendages seen in Pterygotus, etc. (Fig. 8),represent the chelicere,and 
correspond, therefore, to the second pair of antenne in the crustaceans. 
What, then, represents the olfactory antenn in the scorpions? The 
answer to this question has been given by Croneberg, and very strik- 
ingitis. The two olfactory antennz of the crustacean have combined 
together to form a hollow tube at the base of which the mouth of the 
animal is situated, so that the food passes along this olfactory passage 
before it reaches the mouth. This organ is often called after Latreille, 
the camerostome, sometimes the rostrum; it is naturally median in 
position and appears, therefore, to be an unpaired organ; its paired 
