THE EVIDENCE OF THE OLFACTORY APPARATUS 22 1 



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 

 antenna? 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 

 pala?ostracan 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 antenna? are not present, either in the living land-forms or 

 the extinct sea-scorpions, for all the antenna?-like, frequently chelate, 

 appendages seen in Pterygotus, etc. (Fig. 8), represent the chelicene, and 

 correspond, therefore, to the second pair of antenna? in the crustaceans. 



What, then, represents the olfactory antenna? in the scorpions ? The 

 answer to this question has been given by Croneberg, and very strik- 

 ing it is. The two olfactory antenna? 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 



