( 187 ) 

 SUMMARY 



OF CURKENT EESEAECHES RELATING TO 



ZOOLOaY AND BOTANY 



(^principally Invertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS.' 



ZOOLOGY. 



A. VERTEBRATA :— Embryolog-y, Histology, and General. 



a. Embryology, t 



Evolution of the Central Nervous System of Vertebrata.f — Prof. 

 J. Bland Sutton, who has published the suggestion that the central 

 canal of the nervous system may be regarded as a modified portion of 

 bowel, finds support in the opinions of Dr. Gaskell. Prof. Sutton urges 

 that the approximation of the edges of the archenteron of the gastrula of 

 Echinus at one point would produce a thickening and divide the cavity 

 into a dorsal and a ventral portion, the part below corresponding to the 

 bowel or coelom, while the parts on the dorsal aspect would represent 

 the medullary folds of Vertebrata. By occluding the blastopore we 

 should get an arrangement of parts which would correspond in transverse 

 section to what obtains in the early vertebrate embryo, and in longi- 

 tudinal section with the U-shaped tube with which his hypothesis starts. 



This view tends to show that the upgrowths known as the medullary 

 laminae, and the downgrowths forming somatopleure and splanchnopleure 

 represent a modification or an abridgment of the invagination process so 

 universal among Invertehrata. This view of the origin of the central 

 canal absolutely removes the objection that its epithelium is epiblastic, 

 whereas that which lines the gut is hypoblastic. In its simplest form, 

 the hypoblast is that portion of the epiblast which, after invagination, 

 lines the archenteron. According to this view the epithelium of the 

 central canal of the nervous system from the infundibulum of the third 

 ventricle to the extremity of the cord, that lining the neurenteric passage, 

 as well as others, are of hypoblastic origin. 



The discovery of His that the cells which make up the medullary 

 folds are not, as is usually taught, metamorphosed into nerve-cells, but 

 form the sustentaculum of the nervous axis, is an important fact in 

 support of the intestinal origin of the spinal cord. 



* 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 actually 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 Brain, xi. (1888) pp. 336-42. 



O 2 



