l893-] ENTOMOLOGICAL NEWS. 20I 



phagial. The protocerebron. which innervates the eyes is strictly com- 

 parable to that of the Crustaceans, the M\riapods and the Insects; it is, 

 however, to be remarked that in Limuhis the pedunculated body attains 

 proportions truly colossal. This same organ, although modified, is also 

 recognizable in the Arachnids, where it has been described by M. Saint 

 Remy under the name of ' stratified organ.' In the Crustaceans; Myria- 

 pods and Insects, the deutocerebron is entirely pre-cesophagial; it fur- 

 nishes a root to the visceral system and innervates the first pair of cephalic 

 appendages. It is strictly the same in Limulus and the Arachnids, but 

 here the innervated appendages are called chelicerae instead of first pair 

 of antennte. The first pair of antenna? are above all, organs of olfaction, 

 while the chelicerse are only tactile appendages physiologically analogous 

 to the second antennae of the Crustaceans; in Limulus and the Arachnids, 

 the deutocerebron is not differentiated into olfactory lobes.* A tritccere- 

 bron comparable to that of Crustaceans and Insects is wanting in the 

 .Arachnids and Linmlus; in these animals, the first ganglionic mass which 

 follows the deutocerebron is exclusively concerned with the innervation 

 of the mandible (first ma.xilliped in Limulus). The visceral nervous sys- 

 tem of Arachnids and Limulus is represented only by ganglia homologous 

 to the lateral ganglia of Insects and derive their roots from the deutocere- 

 bron; but the ganglia imparia are wanting, their absence being correlated 

 with that of the tritocerebron. The homologies of the nervous system 

 necessarily enter into those of the cephalic skeleton. The chelicerae are 

 evidently the homologues of the antennules of Crustaceans and of the 

 antennae of Insects. The rostrum of Arachnids being innervated by the 

 deutocerebron cannot be completely homologous to the labrum of Insects 

 and Crustaceans, of which the innervation is tritocerebral; the rostrum 

 and the labrum are two analogous formations, but developed on different 

 zonites. ... It results from this comparative examination that the Arach- 

 nids and Limulus ought to be united in a single group opposed to all the 

 other Arthropods. They may be designated under the common name of 

 Chelicerata for the peculiar condition of their nervous system is connected 

 with the absence of olfactory antennae and the replacement of these latter 

 by chelicerae. The Crustaceans, Myriapods, Insects and Peripatus present 

 considerable resemblances between themselves. They can be united 

 under the name of Antehnata to indicate that it is to the existence of olfac. 

 tory antennje that they owe the distinctive traits of their cerebral organi- 

 zation. The Antennata can be divided into two secondary groups : The 

 first comprising only the Crustaceans and characterized by a complete 

 development of the tritocerebron correlated with the existence of a second 

 pair of antennae. The second uniting the Myriapods, Insects and Peri- 



* These considerations of a physiological order have led M. Saint Retny to think that 

 the deutocerebron was not developed in the Arachnids, and that the second cerebral seg- 

 ment of these animals was the representative of the tritocerebron of the Crustacea; but 

 from a strictly morphological point of view this opinion caimot he admitted, the second 

 cerebral segment of the Arachnids having its commissure pre-oesophagial, cannot be com- 

 pared to the tritocerebron, whose commissure is always post cesophagial. 



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