407 



treten, bei welchen eine Intercostalnerveninnervation zu konstatieren 

 ist, wodurch eine von den jetzt genannten fernerstehende Gruppe 

 Sternales noch in Betracht kommen könnte. Eine Verschiedenheit in 

 der Herkunft der Sternales wurde übrigens schon 1876 von v. Barde- 

 leben ausgesprochen. Es ist jedoch nicht unsere Aufgabe, in diesem 

 Zusammenhange die verschiedenen Ansichten betreffs der Deutung der 

 Sternales auseinanderzusetzen und zu beurteilen. 



Nachdruck verboten. 

 The Development of the Hypochord in Raia batis ; 

 with a Note upon the Occurrence of the Epibranchial Grroove 

 in Amniote Embryos. 



By W. T. Gibson, A. R. C. S. 



(From the Zoological Laboratory of Edinburgh University.) 



With 13 Figures. 



This communication upon the hypochord ^) is based upon the study 

 of a series of embryos — already in sections and almost all stained 

 with borax-carmine — lent me by Dr. Beard. For permission to work 

 in the above laboratory, and for many acts of kindness, I am indebted 

 to Professor Ewart. Dr. Ashworth was good enough to draw my 

 attention to a reference in Eisig's monograph upon the Capitellidae, 

 otherwise, in common with other workers, I would have omitted to 

 notice the revision of Eisig's views contained in it. To Professor Meek, 

 Durham University, I owe my knowledge of the existence of Ussofp's 

 paper. 



Not all of the literature professing to deal with the hypochord is 

 reviewed below. Some is considered in the note at the end of this 

 paper for the reason that another structure has been described in 

 error as the hypochord by certain workers. 



Review of the Literature. 



Leydig (25), with Selachian embryos, was the first to mention the 

 hypochord. Misled by unsatisfactory material, as we may be sure, he 

 thought it lay within the notochord. It was compared with a bundle 

 of fibres found by Johannes Müller in the Carps and Cyclostomes. 



1) The clumsier English term "subnotochordal rod" has been dis- 

 carded in this paper in favour of the equivalent of "hypochorda" and 

 "hypocorde", terms which have latterly been used by continental workers. 



