July, 1902] 



PS YCHE. 



369 



as Viallanes and others have shown, the 

 evidence of both comparative anatoni)- 

 and embryology, clearly indicates that 

 the antennae of the Hexapoda are the 

 homologues, not of the sccoiu/, but of the 

 first antennae or antcniiides of the 

 Crustacea. This is evidenced by the 

 fact that the antennae of insects and the 

 first antennae of Crustacea are inner- 

 vated by the deutocerebral ganglia while 

 the second antennae of Crustacea are 

 innervated by the tritocerebral ganglia. 

 The question then is as to whether 

 Latreille was correct in regarding the 

 chelicerae as homologous with the second 

 antennae of Crustacea. 



The evidence at hand leaves little 

 doubt as to the correctness of this view. 

 It is supported not only by comparative 

 morphology but by physiological and 

 embryological data. 



Although physiological evidence may 

 be of doubtful value as a criterion for 

 determining homology it is interesting 

 to note that, as pointed out by St. Remy, 

 the first antennae are primarily olfac- 

 tory organs while the chelicerae, like the 

 second antennae, are primarily tactile 

 organs. 



From the embryological side the most 

 striking evidence has been the discovery, 

 by several investigators, of evanescent 

 appendages lying in front of the rudi- 

 ments of the chelicerae. The most def- 

 inite account of these vestigeal antennae 

 is that of Jaworowski, '91, who discov- 

 ered them in the embryos of Trochosa 

 singoriensis. 



Latreille's theory has been assailed by 



Balfour, 'So, and others on the ground 

 that the ganglia of the chelicerae are 

 primitively suboesophageal, like those of 

 the mandibles of insects and that they 

 only secondarily pass forward to unite 

 with the supraoesophageal ganglia. This 

 argument loses weight when we con- 

 sider the fact that the ganglia of both 

 pairs of anicnnac were primitively post- 

 oral in position. Indeed, Pelseneer, 

 '85, has shown that even in the adult 

 of Apus, a phyllopod, the second anten- 

 nae are innervated by suboesophageal 

 ganglia. Moreover, the studies of Bal- 

 four antedate the establishment of the 

 existence, in insects, of a premandibular 

 segment corresponding to the second 

 antennae and having its ganglia at first 

 postoral. 



A more serious objection has been 

 urged by Viallanes, '93, who believes 

 that the chelicerae are the homologues 

 of .the first antennae. He states that in 

 the adult arachnids the cerebral seg- 

 ment innervating the chelicerae has its 

 commissure entirely preoesophageal and 

 that therefore it cannot be homologous 

 with the tritocerebral or second anten- 

 nal. As bearing on this argument it 

 is interesting to note that Janet, 99, 

 regards the postoesophageal commissure 

 as a compound of fibers from the three 

 primitive commissures of the proto-, 

 deuto-, and tritocerebral ganglia. The 

 argument of Viallanes can also be met 

 by the evidence that both pairs of anten- 

 nae were primitively postoral in posi- 

 tion. If in the crustaceans and insects 

 the deutocerebrum has become entirely 



