Reprinted from the Quarterly Journal of ' Microscopical Science ' for October, 



1891. 



THE FORMATION AND FATE OF THE PRIMITIVE STREAK, 

 WITH OBSERVATIONS ON THE ARCHENTERON AND 

 GERMINAL LAYERS OF RANA TEMPORARIA. 



By Arthur Robinson, M.D., Senior Demonstrator of Anatomy in the 

 Owens College; and Richard Asshbton, M.A., late Demonstrator of 

 Zoology in ike Owens College. 



With Plates III. & IV. 



Even a superficial perusal of the literature of the development of 

 the Amphibian ovum is sufficient to acquaint the inquirer with 

 numerous contradictory statements concerning points of weighty 

 morphological importance. Not only are there differences of opinion 

 as to the interpretation of some of the developmental features which 

 which are generally allowed to be readily recognisable, but there are 

 also assertions, made by different observers, concerning merely the 

 structural arrangement and the fate of various portions of the Amphi- 

 bian ovum which are absolutely irreconcilable with each other. The 

 confusion is increased 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 development, were it not that 

 we think the results of our recent observations on the development of the 

 Anura tend to simplify the problem we have been studying by throwing 

 light upon several interesting developmental phenomena. For these 

 reasons alone are we induced to publish the results of a research which 

 tend to conclusions different from those of our predecessors, whose 

 experience is, in most cases, much more extensive than our own. 



