224 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to excite them by experimental means. Laborious and varied re- 

 searches, directed to this end, have always yielded to him negative 

 results. Since, then, the fibres are non-contractile, can they (he 

 asks) be nervous ? Such a view is plausible and may be true of the 

 fibres which supply the complex marginal lashes of Stylonychia, not 

 to speak of other Infusoria, but can scarcely hold good of ciliated cells 

 in general. In spite of a certain agreement, the differences between 

 intracellular ciliary fibres and true nerve-fibrils are too striking to 

 admit of such an interpretation. Doubtless the origin of the cone of 

 fibres from one trunk-fibre and the way in which they incline towards 

 the cilia offers a very tempting explanation of the isochronous motions of 

 the latter. But do we ever find axis-cylinders which, like these fibres, 

 may be stiff", show double refraction and obstinately resist various 

 strong chemical solvents '? Neither may we conclude that the fibres 

 act as mechanical supports to the cilia ; they are too loosely connected 

 with these, and in the majority of cases too lax and perishable for 

 such a purpose. Most likely is it that the fibres contribute to the 

 nutrition of the cilia, supplying the materials needed for the dis- 

 charge of their function and the renewal of these active and short- 

 lived filaments. 



Finally, Engelmann refers to the presence of a fibrous structure in 

 various non-contractile secreting cells. Most notably do the cells 

 lining the ducts of the spinning glands of the silkworm, as described 

 by Lidth de Jeude,* resemble in this respect ciliated cells by their 

 optical no less than their more obvious structui-al characters. The 

 discovery by Max Schultze of filaments in the outer moiety of the 

 inner segments of the retinal rods and cones also aids him in re- 

 butting the assumption that the intracellular fibres of such structures 

 can subserve a merely mechanical office. 



We have said little of the reagents used by Engelmann in these 

 refined observations. To those who study methods as well as results, 

 his essay is indispensable. His recommendations of green light and 

 of an apparatus which guards the eye from disturbing rays are too 

 valuable in practice to be neglected. 



Central Nervous System of Reptiles and Batrachians.f — Dr. 

 J. J. Mason deals with the form of the spinal cord, and especially 

 that of its enlargement ; the nuclei of the nerve-cells, and variations 

 in their shape, size, &c., in the same individual ; the number of 

 ganglionic bodies in the spinal cord, and their relations to the roots 

 of the spinal nerves, and the difference, if any, which may be deter- 

 mined by sex. After stating the methods of preparation of his 

 sections. Dr. Mason gives the following as the result of very extended 

 examinations of a large number of sections of the spinal cord of the 

 frog and different reptiles. 



1. The central canal of the spinal cord of frogs is more nearly 

 cylindrical in shape than has been generally supposed. The oval 



* See this Journal, ii. (1879) p. 297. 



t ' Journ. of Nervous and Mental Disease,' Chicago, 1880, 8 pp. ; Amer. 

 Natural, xv. (1881) p. 50. 



