32 DR. G. C. BOURNE ON THE RAN[NXD.E : 
less with the Crayfishes, because in the first-named the thoracic connectives 
are separate and show but little tendency to lateral fusion. But of all the 
Macrura they most closely resemble Nephrops in this and other respects. 
In both the subcBsophageal gauglion mass is in a very similar state of con- 
centratioUj the differences being that in Ranina the mandibular nerves are 
given off from the circum-oesophagCiil connectives (this may be correlated 
with the great lenglli of these connectives) and in Nephrops the ganglion 
pair of the third maxillipeds retain a certain distinctness. The connectives 
between the subcesophageal and the ganglion-pair of the chelipeds are very 
nearly of the same length and in the same condition of incipient lateral 
fusion in Nephrops as in Notopus, though the concentration is carried further 
in the lateral sense in Lyreidus and in the longitudinal sense in Ranina. 
The connectives between the ganglion-pairs of the chelipeds and first 
pereiopods are much longer in the Raninidse than in Neplirops, but are 
equally distinctly paired in both and show no tendency to lateral fusion.. 
The sanie may be said of the connectives next following. In the Raninidse 
the last two thoracic ganglion-pairs are more {Lyreidus) or less {Ranina) 
closely fused together. These differences apart, if the long chain of six 
abdominal ganglion-pairs of Nephrops were shortened up to the condition 
found in the Ranfnidse and withdrawn into the thorax, there would be very 
little difference between the two nervous systems. So far, then, as this part, 
of their anatomy may serve as a guide, the Dromiacea have progressed 
further from the Macrurous in the direction of the Brachyurous type than 
have the Raninida?, but the latter retain many distinct Macrurous features- 
and exhibit specially close affinities with Nephrops. 
It will be noticed that there is a marked tendency for the thoracic ganglia 
to form two groups, one at the anterior the other at the posterior end of fh& 
thorax, in the Raninidre. This must be correlated with the powerful develop- 
ment of the first, second, and third pereiopods as digging or swimming- 
organ?. These limbs are exceedingly strong, and are actuated by largely 
developed muscles enclosed in remarkably deep cavities formed by the endo- 
phragnial skeleton. The size and extent of these muscle cavities as compared 
with those of other Brachyura is one of the most striking features when one- 
undertakes a dissection ot any member of the Raninida?, and the abundant 
musculature of the limbs makes the dissection of the neivous system difficult.. 
It is also worthy of remark that in Lyreidus the last pair of pereiopods are 
very weak and attenuated and the corresponding ganglion-pair is practically 
unrecognizable, whereas in Ranina, in which the last pair of pereiopods 
differs little in size from the rest, its ganglion-pair is distinct and emits. 
large nerves to the limbs. 
Two good figures are given in Cuvier's 'Regne Animal,' but otherwise 
de Haan is the only author who has dealt with the endophragmal skeleton of 
