360 SUA] MARY OF CURRENT RESEARCHES RELATINft TO 



SUMMARY 



OF CURRENT RESEARCHES RELATING TO 



ZOOLOGIY AND BOTANY 



(^principally Invertehrata and Cryptogamia^, 



MICKOSCOPY, &c., 



INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS.' 



ZOOLOGY. 



A. VERTEBRATA: — Embryology, Histolog-y, and General. 



a. Embryology.t 



Origin of Nervous System of Vertebrates.^ — Dr. W. H. Gaskell, 

 after a discussion of the relation between the structure, function, distri- 

 bution, and origin of the cranial nerves, propounds a new theory of the 

 origin of the nervous system of Vertebrates ; any theory that shall be 

 satisfactory must take into account not only its segmental arrangement 

 but also its tubular formation. If we fix our attention exclusively upon 

 the nervous elements of the central nervous system v/e can describe it 

 as a system composed of a bilateral chain of ganglia connected together 

 by means of longitudinal and transverse commissures, which gives origin 

 to a series of segmental nerves, and is connected by means of well- 

 defined commissural tracts with another nervous system of higher 

 function, which gives origin to no outgoing nerves, except such nerves 

 of special sense as the optic and olfactory. In addition, however, to its 

 nervous elements the spinal cord contains an elaborate system of non- 

 nervous structures, viz. the supporting structures of the cord, and the 

 folding over of the medullary jjlates gives origin not merely to nervous 

 material but also to a tiibe of supporting tissue, which was originally 

 formed of compact layers of epithelial cells arranged symmetrically 

 around the central canal. Dr. Gaskell thinks that, in the embryological 

 development of the central nervous system, we are observing the 

 simultaneous development of two different organs, the one the nervous 

 system, and the other the tube of supporting tissue, the formation of 

 which is not necessarily involved with that of the nervous system. In 

 certain parts of the central nervous system the sole structure formed by 

 the folding over of the medullary plate is the supporting tube which is 

 not and never was nervous, while in other parts the simultaneous forma- 

 tion of nervous material with that of the supporting tube has so compli- 



* The Society are not intended to be denoted by the editorial " we," and they do 

 not hold themselves responsible for the views of the authors of the papers noted, 

 nor for any claim to novelty or otherwise made by them. The object of this part of 

 the Journal is to present a summary of the papers as actualt;/ published, and to 

 describe and illustrate Instruments, Apparatus, &c., which are either new or have 

 not been previously described in this country. 



t This section includes not only papers relating to Embryology properly so called, 

 but also those dealing with Evolution, Development, and Reproduction, and allied 

 subjects. X Journ. of Physiol,, x. (1889) pp. 153-211 (5 pis.). 



