FORMATION AND FATE OF THE PRIMITIVE STREAK. 451 



The Formation and Pate of the Primitive 

 Streak, with Observations on the Archen- 

 teron and Germinal Layers of Rana tem- 

 poraria. 



By 



Artbur Robinson^ m.D., 



Senior Demonstrator of Anatomj in the Owens College ; 



and 



Ricbard Assbeton, in. A., 



Demonstrator of Zoology in the Owens College. 



With Plates XXXIV and XXXV. 



Even a superficial perusal of the literature of the develop- 

 ment of the Amphibian ovum is sufficient to acquaint the in- 

 quirer with numerous contradictory statements concerning 

 points of weighty morphological importance. Not only are 

 there diflFerences of opinion as to the interpretation of some of 

 the developmental features which are generally allowed to be 

 readily recognisable, but there are also assertions, made by 

 different observers, concerning merely the structural arrange- 

 ment and the fate of various portions of the Amphibian ovum 

 which are absolutely irreconcilable with each other. The con- 

 fusion is added to by a loose application of terms describing 

 changes and areas, so that it becomes difficult to decide the 

 exact relation that the Amphibian ovum bears to the ovum of 

 other Vertebrates. 



In view of the chaos which already exists we would not 

 readily enter upon any further discussion of Amphibian 



