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 Ainphipoda consists of supra- 

 oesophageal or cerebral ganglia, united by commissures with 

 an infra-oesophageal 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 Hve or six 

 pairs of abdominal ganglia. In some Isopoda ( Cymothoa^ 

 idotea) th.e abdominal ganglia are also distinct; but in others, 

 such as u^ga bicarlnata (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 Cymothoadm 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 Lmmo- 

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

 of post-oesophageal 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 Oniscidm. 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 Edriophtlialmia^ though 

 the fine setfe 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 

 aggreacated ocelli of Lmmodipoda^ and of many Isopoda and 

 Amphipod/i^ to the strictly compound eyes, as complex as 

 those of the highest Articxdata^ which exist in uUga and in 

 PhrosiJia. 



The female genitalia of the Edriophthalmia consist of two 

 simple sacs, the ducts of which usnally 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 caeca 

 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. 



» " Histoire Naturelle des Crustaces," vol. iii., p. 187. 



