188 DESCRIPTIONS OF PREPARATIONS. 



exception of the terminal ganglion, which may be seen to give off a large 

 number of nerves. Accurate investigations have shown that of these 

 there are five pairs and one posterior, median and azygos nerve. This 

 azygos nerve supplies the termination of the intestine ; and the nerves to 

 either side of it, i. e. the fifth or innermost pair, are destined for the telson. 

 The two outermost pairs of nerves, i. e. the first and second, go to the 

 exopodite, and the third pair to the endopodite of the last enlarged pair 

 of swimmerets. The fourth pair, according to Krieger, supplies muscles 

 in the same manner as do the commissural pairs of nerves corresponding 

 to the five foregoing ganglia. 



The infra-oesophageal and the thoracic ganglia lie in the sternal canal 

 formed by processes of the apodemata. The roof of this canal has been 

 cut away to expose the nerve chain, but parts of the apodemata may be 

 seen on either side of it in the shape of vertical tubular processes. 



The two eyes with their stalks, the bases of the first and second 

 antennae, are shown by the removal of the overhanging rostrum. The 

 surface of the basal joint of each first antenna thus exposed is the one 

 that contains the aperture into the auditory sac. The aperture itself is 

 concealed by setae. 



The summits of the branchial plumes are well seen in this specimen 

 between the branchiostegite and the epimera of the thoracic somites. 

 From the internal aspect of the epimera, the muscles which move the 

 limbs upon the thorax are seen trending downwards and bifurcating as 

 they pass between the sections of the endophragmal skeleton to their 

 insertions. 



The sub-oesophageal ganglion gives off six inferior and four superior or dorsal 

 nerves. The six inferior are destined for the mouth-parts. The mandibular nerve 

 accompanies the commissures round the oesophagus for a certain distance. The 

 last nerve, which goes to the third maxilliped, arises at some distance behind that 

 for the second maxilliped, and the part of the ganglion from which it springs has a 

 certain amount of distinctness or individuality. Of the four superior nerves the 

 first is of considerable size and innervates the scapho-gnathite. The three remain- 

 ing nerves are fine, and their destination unknown. 



Each of the five thoracic ganglia gives off two pairs of nerves : an anterior large 

 pair destined for the limb and the gills belonging to the somite, and a posterior fine 

 pair destined for the corresponding thoracic muscles. 



The median azygos nerve given off by the last abdominal ganglion divides, ac- 

 cording to Lemoine, into two branches, a posterior anal branch and an anterior 

 intestinal branch. The latter subdivides into (i) a branch to the anal end of the 

 intestine ; (2) a branch which courses along the ventral surface of the intestine, to 

 which it gives twigs from spot to spot and (3) a branch which turns round the in- 

 testine and runs upon its dorsal aspect. Lemoine traced these two last-mentioned 

 branches as far forwards as the genitalia. 





