^ NOTES AND MEMORANDA. 77 



animals, among the Sadiata particularly, belongs or not to the nervous 

 system. Certain authors, moreover, have taken their stand on the 

 diflferences which the nerve elements present in Invertebrata and 

 Vertebrata to mark further the separation which exists between these 

 two divisions of animals. 



The nerves of Decapod and other Crustacea, in spite of their bulk, 

 are difficult to study, by reason of the rapidity with which these elements 

 alter when they are isolated or dead, or are brought into contact with 

 any reagent. The nerves of the ganglionic chain and the peripheral 

 nerves jDresent identical characters. They are formed by bundles of 

 nerve-tubes enveloped in a sheath of very thick perineurine. 



Each of these tubes is composed of a sheath of a homogeneous 

 amorphous substance, the contents of which are soft, easily changeable, 

 sometimes homogeneous, sometimes either finely granular, or striated 

 longitudinally. These tubes are very volumLuous. Their diameter 

 varies from -01 mm. to -08 mm. and -09 mm. Notwithstanding that, 

 all the cylinder of the substance or soft fibre which fills the amorphous 

 sheath of the nerve-tubes of the Crustacea corresponds to the single 

 cylinder-axis of the nerve-tubes of the Vertebrata, an idea already 

 propounded, but in a rather doubtful manner, by Leydig. The 

 myeline is wanting, and its absence leaves the essential microscopical 

 filaments of the nerves with their transparency and their paleness, 

 whence the difficulty of seeing them by transmitted light as with the 

 naked eye. Our * researches show that there is identity of substance 

 between the cellular body of the ganglionic cells and the contents of 

 the nerve-tube starting from the ganglia. 1st, the large cells of the 

 ganglia which attain the size of oue-fifth to one-fourth of a millimetre, 

 have prolongations very nearly as large as the largest peripheral nerve- 

 tubes into which we succeeded in following them, as so many fibres 

 filling the tube or homogeneous sheath ; 2ad, immediately after death 

 sarcodic atoms are formed in the cells and in the substance of the nerve- 

 fibres, gradually bringing about the decomposition of both into granular 

 masses of identical appearance ; 3rd, nitric acid, alum, and perchloride 

 of iron produce at the same time coagulation of the body of the cells 

 and the contents of the tubes. Nitric acid, particularly, gives an 

 absolutely conclusive reaction ; it retracts the substance of the 

 nerve-fibres, and produces a very distinct and regular longitudinal 

 striation ; the same striation is seen on the cells and their immediate 

 prolongations.! 



* M. Cadiat, in ' Coraptes Rendus,' vol. Ixxxvi. p. 1420. 



t This is diflScult to demonstrate among the Vertebrata ; and it has been 

 Eought for in many ways, becau-e it is important to physiology to know if each 

 cylinder axis is a bundle of nervous conductors. In the Crustacea, particularly in 

 the Uraiu squi7iado, this situation is very evident. On the ganglionic chain of 

 larva of Libelluki are found nerve-tubes identical with those of the Crustacea. 

 But, in the insects, the sheaths of Schwann are very fine and frao-ile, and under 

 the influence of the least pressure or of a liquid having sufficient osmotic power, 

 all the tubes enclosed in the same sheath of perineurine break and leave a graimlar 

 residue scattered over with nuclei. This granular matter, under the influence of 

 alum and carmine, takes exactly the same tint and the same appearance as the 

 masses which surround the nucleus of the nerve-cells. In the Leech, Dytiscus, 

 and Hydrophiius we have obtained analogous results. 



