Ada Acad, Naturae Curiosa Bounce. 587 



more pointed manner, opposing vertebral animals with a double 

 nervous system ; (Diploneura,) to invertebral, with a single nervous 

 system, (Haphlonmtra ;) and dividing the latter again into Ganglia* 

 neura and Mydoneura, according as they resemble, on the one 

 hand, the ganglionic system of the sympathetic nerve, or, on the 

 other, approach to the type of the spinal marrow. 



At a later period, G. Treviranus and E. Weber assimilated the 

 series of ganglia in insects to the ganglia of the spinal nerves, 

 and viewed the connecting cord as the first rudiments of a spinal 

 marrow. Still more recently, when the supposed analogy between 

 the sympathetic nerve and the ganglionic chain of insects had been 

 Jong refuted and abandoned, Serres arid Desmoulins, who have so 

 freely, and with such inadequate acknowledgment, availed them- 

 selves of the researches of the Germans, again raised the hypothesis 

 from oblivion, without adverting to, and apparently without being 

 acquainted with, what had already been done by the eminent men 

 above alluded to. 



Previous to the attempt to decide the whole question by the de- 

 scription of a sympathetic nerve in insects, distinct from the abdo- 

 minal chain of ganglia, Dr. Mueller attempts to determine the 

 essential characters of a spinal and a sympathetic system, abstracted 

 from the accidental circumstances of form, position, &c. 



A nervous system, consisting of separate ganglia, is not, there- 

 fore, necessarily equivalent to the sympathetic system of vertebral 

 animals; neither is that always a spinal marrow which presents 

 itself in the shape of a chord. These circumstances of arrangement 

 are of little importance, and are mainly determined by the shape 

 and peculiar organisation of the animal, in some vertebral animals, 

 Tttrodon mola, for instance, all the nerves of the trunk arise from 

 (he medulla oblongata, the separate nerves contained within the 

 spinal canal, representing what, in other cases, is the spinal marrow. 

 Jn Lophius piscatorius, the spinal marrow terminates in the upper 

 cervical vertebrae, the nerves, which here, as in the former case, 

 arise by double roots, running separate and parallel through the 

 spinal canal. 



On the other hand, there are articulata which do not possess the 

 usual ganglionic chain. Thus, according to G. Treviranus, the 

 ganglia of the phalangidae are dispersed as in mollusca, whilst in 

 the true arachnidae the nervous system forms a solid central cord, 

 and in scorpions assumes the usual character of a chain of ganglia. 

 Even as regards the sympathetic nerve itself, the presence of ganglia 

 is by no means an essential character, for in most fishes they are 

 altogether wanting. 



. The only absolute distinctive characters of the two nervous systems 

 of the trunk are, that the spinal marrow is chiefly destined to pre- 

 side over voluntary motion, whilst the sympathetic nerve is exclu- 

 sively devoted to the viscera ; that the former is an immediate con- 

 tinuation of the brain, whilst the latter has an independent develop- 

 ment, except as regards the filaments by which it is connected with 



