300 A HISTORY OF RECENT CRUSTACEA 
lateral angles of the carapace close it in only at the sides 
and not in front. | 
The marsupium of the female is formed by the splitting 
of the ventral wall of the segments which carry the third 
maxillipeds and the first three pairs of perzeopods, the 
upper lamina separating the pouch from the general body- 
cavity. Only in the aberrant Isopod genus Gnathia 
(wrongly called Anceus) has any correspondent arrange- 
ment for the marsupium been observed, although there the 
ventral wall serves the purpose without being split into 
two lamine. 
The body contains an oval or spindle-shaped heart, ex- 
tending from about the middle of the carapace back 
through two or three of the free segments. It has one 
pair of lateral venous openings. At the sides of it are two 
elongate organs with some excretory function. The liver- 
tubes are usually three pairs, but there is only a single 
pair in the family Campylaspide. The nervous system 
comprises the supracesophageal ganglion or brain, and 
sixteen ganglia, of which the first three in close contiguity 
innervate the parts of the mouth. The next seven belong 
to the trunk and are connected by rather long double 
commissures. The remaining six, pertaining to the pleon, 
are weakly developed, and their connecting commissures 
are very long and slender. 
It isa rather singular circumstance that the telson is 
large and conspicuous only in two out of the eight families. 
In one other family it is distinct, but small and without 
spines. In the remaining five families it is entirely want- 
ing, except so far as the ventral opening may vouch for its 
existence, and a slight prolongation of the sixth pleon- 
segment may suggest that it is not wholly lost but 
coalesced. 
Of the characters given the combination of avery few 
will suffice to distinguish the Cumacea from all other 
Edriophthalma. 
