ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 603 



seen small highly refractive granules, which " undoubtedly owed their 

 origin to nutrient matters taken into the interior of the cell." The 

 author is of opinion that in the Turbellaria and Ccelenterata (inclusive 

 of Sponges) intracellular digestion is the general rule ; a very suitable 

 form for its demonstration is stated to be young Ctenophores, for in 

 them the whole process can be followed out to the end (i. e. till the 

 time when crystalline concretions appear within the vacuoles) in one 

 and the same individual. The opinion of Krukenberg that colouring 

 matters are indigestible, is not supported by the author's observa- 

 tions, carmine, for example, being distinctly absorbed ; and Eisig 

 has lately shown that carmine is digested in the intestinal canal of 

 the Capitellida? and excreted by their segmental organs. Some other 

 remarks of Krukenberg are closely criticized, and are regarded by 

 Metschnikoff as not really affecting the reality of intracellular 

 digestion in the lower forms. 



Mollusca. 



Nervous System of Mollusca.* — W. Vignal finds that the nerves 

 are surrounded by a sheath of connective tissue of some thickness, 

 which is formed of imbricated lamellae, containing a number of 

 nuclei ; in the terrestrial pulmonate Gasteropoda the true sheath is 

 invested in a second, formed of a layer of vesicular cells, which is not 

 however, proper to the nerves, as it is found also on the vessels. 

 From the true sheath there are given off a number of partitions, made 

 up of several lamella?, which pass towards the centre of the nerve ; as 

 they do so the lamella? divide afresh and unite one with another to 

 form spaces of various sizes, in which we find the axial portion of the 

 nerve-fibrils, and the protoplasm which surrounds them. While there 

 are a number of nuclei in the partitions there are none in the proto- 

 plasm : the sheath is not to be compared with the sheath of Schwann 

 in the Vertebrata, but if it is to be compared with anything found in 

 that phylum, it must be with the intrafascicular connective tissue. 

 This peculiar structure of the envelope of the nerve-fibres is, it is 

 remarked, found very generally among the In vertebrata, something 

 analogous being found in both Hirudinea and Lumbricida?. Its 

 presence affords an explanation of the difficulty of dissecting out any 

 length of nerve-fibrils. These fibrils themselves spread over the 

 surface of the ganglia and penetrate some way into their interior ; in 

 this region the protoplasm contains a number of fatty and pigmented 

 granulations, which would appear to form a reserve used up by the 

 animal in the winter, as they are much more numerous (in Helix) 

 during the summer than they are at the end of the period of 

 hibernation. 



The author finds that for the demonstration of the partitions 

 chloride of gold is the best reagent, for they are coloured by it while 

 the nerve-fibres are almost unstained ; if the section is then decolorized 

 by cyanide of potassium, and afterwards treated with picro-carminate 

 of ammonia, the nuclei are very easily seen. The fibrils are best 

 demonstrated by a mixture (in equal parts) of osmic and chromic 



* Comptea Rendus, xcv. (1S82) pp. 249-51. 



