628 RECORD OF CURRENT RESEARCHES RELATING TO 



delicate. The author finds no evidence that the former arc compounds 

 of the latter ; and in this he is supported by Hclmholtz, Haeckel, 

 and Yung. Two of the fibres of the longitudinal commissures are 

 especially distinguished by their size ; these are the " colossal " 

 nerve-fibres. Krieger has been led by his observations to regard the 

 bundle of fine fibres which were first described by Eemak as placed 

 in these to be merely coagulation-products. When carefully prepared, 

 the contents of the colossal fibres may be seen to be clear and homo- 

 geneous, but after a period of removal from the body delicate striations 

 appear, and gradually become more distinct. 



Dotted Substance. — Even with the naked eye, in the fresh con- 

 dition, it is possible to see in the ganglia of the crayfish whitish 

 spheres of a comparatively considerable size ; when these are examined 

 under the Microscope, they are seen to be neither ganglion-cells nor 

 fibrous bundles, but rather to consist of a finely granulated mass ; this 

 dotted substance is by Krieger, as by Leydig, Dietl, and others, 

 regarded as being a network of very delicate fibres. The true 

 characters of the body may be demonstrated by two difierent methods. 

 Of these, one is due to Dietl, and consists in making fine trans- 

 verse sections of a ganglion which has been hardened in " osmium " ; 

 the other method is thus described : A portion of a ganglion is placed 

 for several days in a 0*1 per cent, solution of chromate of ammonia, 

 is then teased up with fine needles, and placed under a covering glass 

 in the same fluid. After a brief description of the connective tissue, 

 the author passes to (2) The Topographical relations of the Nervous 

 System. 



Cerebrum. — When we examine this in transverse sections, wo first 

 meet with the two optic nerves ; here, two kinds of fibres can be easily 

 distinguished, one of which is much more delicate than the other. 

 The fine fibres appear to decussate completely, and not to form a 

 semi-decussation, as has been stated by Dietl. In the anterior enlarge- 

 ments of the cerebrum there are some structures which are not 

 easily comprehended ; the first of these is a band of coarse dotted 

 substance, which intervenes between the two pairs of spheroidal 

 bodies which are placed near the chiasma, and the other consists of a 

 pair of rounded bodies, which are made up of a fine dotted substance 

 placed below the just-mentioned spheres. 



Passing to the oesophageal commissures and their ganglia, the 

 author points out that the former are made up of fibres, which arise 

 from the dotted substance of the anterior and posterior swellings of 

 the cerebrum. After giving a careful description of the ganglion 

 and of the nerves which are given ofi" from it, he passes to a considera- 

 tion of the difierent parts of the ventral chain ; he here enters into 

 great detail, which it would be impossible to make clear without a 

 rcj)roduction of the figures by which they are illustrated. 



Influence of Acids and Alkalies on Crayfishes.* — M. Eichet 

 commences by pointing out the impossibility of subjecting air-breathing 

 animals to the influence of acids or alkalies. On the other hand, the 



* ' ComptcH lleuduci,' xc. (18S0) p. 1166. 



