THE NERVOUS SYSTEM. 65 



pairs of ganglia in the Tipulidcc, of which the last is a complex of two pairs, 

 and Leuckart figures eleven pairs in the embryo of the Pupiparaj at an early 

 stage of development (PI. II., Fig. 8). At a subsequent stage only nine 

 remain— the penultimate and antepenultimate pair have disappeared (PI. II 

 Fig. 9)- ' '' 



In the newly-hatched larva of the Blow-fly I have only detected evidence 

 of the existence of six pairs, but ten pairs of nerves arise from the united 

 ganglia. 



It appears to me that the number is reduced, either by complete fusion of 

 two or more, only in certain cases, and that in others the missing ganglia 

 have undergone complete atrophy. As one centre often gives off at least 

 two, and often three pairs of nerves, I do not regard the numbers of pairs of 

 nerves as evidence of the persistence of a similar number of ganglia. 



There are apparently never any ganglia developed in the last abdominal 

 metamere— Weismann's twelfth segment, my fourteenth and fifteenth somites. 

 Weismann demonstrates this in 'Chironomus' [2, p. 38], and adduces it 

 as an argument against Zaddach's hypothesis that a pair of primitive ganglia 

 is developed in each somite [2, p. 83]. 



The Splanchnic Nervous System (PI. II., Fif^s. i and 2) was 

 first detected and figured by Swammerdam [4], and has been 

 carefully studied by J. Miiller,* J. J. Brandt.f Newport [9], and 

 more recently by Bruno Hofer.I It is highly developed in the 

 cockroach ; and exhibits considerable modification, and attains 

 great importance in the larva of the Blow-fly. 



It consists of two single median and of two pairs of lateral 

 principal ganglia. 



The median ganglia are the frontal and proventricular ; they 

 are united by a single thick nerve-cord, which lies immediately 

 upon the dorsal surface of the oesophagus. This is the median 

 or stomogastric nerve. 



The lateral gangha consist of an anterior and a posterior 

 pair. They are connected with the crura of the pre-oral 

 centres, with each other, and with the stomogastric trunk by 

 plexiform nerves, and they supply the labial salivary glands — 

 (B. Hofer). 



The nerves of the splanchnic system arise from these 

 ganglia and from the stomogastric nerve, and terminate in 



* Nova .'Vcta, K. L. C. Acad., Bd. xiv., p. T},. 

 t ' Oken's Isis,' 1831, p. 1103. 



X ' Untersuchungen ii. den Bau der Speicheldrtisen u. d. dazu gehorenden 

 Nervenapparats von Dlatta.' Nova Acta, K. L. C. Acad., Bd. li., 1S87. 



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