362 SUMMARY OP CURRENT RESEARCHES RELATING TO 



posterior opening. Examination of tlie infundibular region (or that 

 where the notochord and the nervous tissue which corresponds to the 

 infra-oesophageal ganglia terminate) of an adult sheep has led Dr. 

 Gaskell to the discovery of what he believes to be the remains of the 

 terminal oesophageal tube. Sections revealed the existence of a canal 

 leading from the cavity of the infundibulum towards the corpus 

 mamillare ; this canal lies quite on the surface of the brain, and occu- 

 pies the greater portion of the length of the tuber cinereum ; it is lined 

 with epithelium continuous with that of the third ventricle and of the 

 infundibulum; its walls are composed of substance similar to the 

 substantia centralis gelatinosa ; the further away it is from the infundi- 

 bulum the more is its cavity closed by the approximation of its walls, 

 and it vanishes at the very surface, completely closed. Its appearance is 

 exactly that of an open tube which has been bent down on the surface 

 of the brain, so that its open extremity became obliterated by the coming 

 together of its walls. The skate, the dogfish, and the lamprey have 

 been all found to have this tube. Dr. Gaskell suggests tbat the terminal 

 part of the oesophagus has been obliterated by being folded down on 

 the infra-oesophageal ganglia, while the next portion of the oesophagus 

 has been dilated to form tbe infundibulum with the glands of the 

 pituitary body lying on the anterior lip of the original mouth or oeso- 

 phagus. Dohrn's picture of the nervous system of a young Limulus is 

 given to illustrate the author's meaning. 



This view brings the vertebrate nervous system into complete harmony 

 with that of Invertebrata, and supports the views of Owen, Balfour, 

 Dohrn, and others. For the present the author says nothing as to the 

 origin of the present alimentary canal of Vertebrates, but he promises to 

 discuss the question shortly. 



Protovertebrae and the Segmentation of the Vertebral Column '— 

 Prof. V. V. Ebner discusses the developmental relations of the proto- 

 vertebrae and the vertebral column. The material worked with consisted 

 mainly of embryos of the ringed snake. Eemak, it will be remembered, 

 derived the vertebrae from the protovertebrae by secondary segmenta- 

 tion; according to His the protovertebrae are " archiblastic," giving 

 origin to muscles, &c,, but without any share in forming the "parablas- 

 tic " skeleton. Both views have had their supporters. Von Ebner 

 corroborates the view of Eemak, and describes how his sections will 

 only admit of this interpretation. Remak's conclusion is to be cor- 

 rected in this point, " that the segmentation of the vertebral column 

 does not arise from a uniform blasteme of the protovertebrae, but appears 

 at a time when the latter are still independent complexes of embryonic 

 cells." He gives several interesting figures of the intervertebral cleft 

 in the protovertebras, which " being very delicate, and often hardly 

 demonstrable, appears to have been hitherto overlooked." 



Study of a Human Embryo-f — Dr. C. Phisalix has had the oppor- 

 tunity of making a study of a human embryo, 10 mm. long. He has 

 discovered a certain number of new facts with regard to the cranial 

 nerves and the central nervous system, the arrangement of the valves 

 and septa of the heart, the origin of the pancreas and the WolflBan body. 

 Additions and corrections have been made to many of the statements of 



* SB. K. Akad. Wiss. Wien, xcvii. (1889) pp. 194-206 (2 pis.). 

 t Arch. Zool. Expe'r. et Gen., vi. (1888) pp. 279-350 (6 pis.). 



