316 THE ANATOMY OF INVERTEBRATED ANIMALS. 



branchia, having its longitudinal canal in communication with 

 the atmosphere by a longitudinal stigma. The fifth pair of 

 abdominal members are rudimentary, while the sixth consti- 

 tute the door-like triangular valves covering the anus, and all 

 the inferior face of the last abdominal segment." ' 



The nervous system in the Amphipoda consists of supra- 

 cesophageal or cerebral ganglia, united by commissures with 

 an iiifra-cesophageal mass, whence commissural cords pass un- 

 der the endophragm to the anterior of the thoracic ganglia, of 

 which there are commonly seven pairs, succeeded by five or six 

 pairs of abdominal ganglia. In some Isopoda (Cymothoa, 

 Idoiea) the abdominal ganglia are also distinct; but in others, 

 such as u^Ega bicarinata (according to Rathke), they are 

 fused into a single mass placed in the anterior part of the 

 abdomen, presenting only traces of a division into five por- 

 tions. In the Cymothoadce and terrestrial Isopoda, again, the 

 abdominal ganglia appear to have completely coalesced with 

 the last thoracic ganglia and form a mass, whence the ab- 

 dominal nerves radiate. Finally, in the short-bodied Lcemo- 

 dipoda, such as Cyamus, there are not more than eight pairs 

 of post-cesophageal ganglia, the posterior commissures of 

 which are so shortened that the nervous system ends in the 

 antepenultimate somite. 



Brandt describes splanchnic ganglia like the lateral pair of 

 Insects in the Oniscidce. It is one of the many respects in 

 which the Isopoda simulate Insecta. 



No other organs of sense than eyes have, as yet, been cer- 

 tainly demonstrated to exist in the Edriophthalmia, though 

 the fine setae which beset the antennary appendages have 

 been supposed to be organs of the olfactory sense. The eyes 

 vary in their structure, from the simple, more or less closely 

 aggregated ocelli of Lmmodipoda, and of many Isopoda and 

 Amphipoda, to the strictly compound eyes, as complex as 

 those of the highest Articulata, which exist in JEga and in 

 Phrosina. 



The female genitalia of the Edriophthalmia consist of two 

 simple sacs, the ducts of which usually open on the ventral 

 surface of the antepenultimate thoracic somite, or on the bases 

 of the limbs of this somite. In the male, one or more casca 

 on each side constitute the testis, which ordinarily opens on 

 the last thoracic or first abdominal somite, in connection with 

 one or two pairs of copulatory organs developed from the an- 

 terior abdominal somites. 



1 " Histoire Naturelle des Crustacds," vol. iii., p. 187. 



