PHYSIOLOGICAL SERIES. 



although other co-ordinated movements of the limbs cm 



-till tukr place. The rest of the ventral-chain ganglia 



thoracic and -i\ abdominal) an- tran-\er>ely con- 



. hut longitudinally widely -eparatcd. They arc 



My, ami each gives off a pair of nem- to 



the u|i|iendages of its segment, and a second pair to the 



bUiiring trunk-muscles. In the abdominal region, a 



third pair of purelv motor nerve- ari-e from the connectives 



Miind each ganglion and are distributed to the great 



abdominal nV\<>r. The terminal ganglion innervates the 



6th abdominal segment and the telson ; it also gives off a 



small rectal nerve, probably comparable to the median 



nerve in the ventral eord OJ 



The connectives of the ventral chain share in the lateral 

 concentration -een in the ^an;lia; in the thorax they lie 

 df l>\ -{! ami (except Ix'twrcii t lie t hird and t'ourt h <;an^lia 

 \\li.-n- the eternal;. -ses between them) are hound up 



in a eommon ncuri lemma-sheath. In the abdomen they are 

 closely oontJgu i in-. The gangiion-cellB of the central system 

 . . md vary much in size, from large pear- 

 sluijHHl <-i IU "2 mm. in diameter t<> <^:\ ML:! ionic nuclei, in which 

 the nucleus is surrounded by a mere film of protoplasm. 

 Tin* latter (x-ciii alwa\> in ma-.- in connection with certain 

 dffinit" j art* of the ei-ntral -v-iem e.g., the globnli and 

 a restricted area of the >ul><i-<>|>lia<jcal ganglion. The 

 nenrefibres drriv.-d iVm ganglion-cells that lie within the 

 central system are tubular, with a thick netiroglia-sheath 

 (in which myelin may occur) containing a semifluid sub- 

 Stance. After 1.-:, \ing the ganglion-cell they give off a 

 few latiTal twig*, that break up in the n.-uropilc and provide 

 a numn- .>n ln;tween the dillen-nt nerve- 



then passes either directly into 



Otte of the |M>ripluTal nervi- and i- di>tributcd to the 



tnUAcU*, or run.-* within one of the connective- to a neigh- 



listant ganglion and there breaks up in the 



neuroplle. The senwiry fibres are very delicate; they 



arise, BJ in Worn 1U in or elo-e beneath ihe skin, 



and enter the ganglia as part of a peripheral nerve. 



"ii they divide into iinirriiir and po.-h-rior 



