Contributions to the Morphology of Cyclostomata. 



II.— The Development of Pronephros and 

 Segmental Duct in Petromyzon.^^ 



By 



S. Hatta, 



Professor in the College of Peei's, Tokyo. 



With Plates XVII- XXL 



The following pages contain the second of a series of 

 studies on the later stages in the development of Petromyzon, the 

 first having already been published some time since in this 

 journal ('97, vol. x, pp. 225-237). 



Our knowledge of the earliest development of the excretory 

 organs in the lampreys is still somewhat incomplete. This 

 circumstance is, I believe, mainly due to the want of recent 

 investigations upon the subject. Since the appearance of the 

 works by Müller (75), Scott ('82), Shipley ('87), Goette 

 ('88), KuPFFER ('90), and others, ten years or more have 



1) It was my intention to publish this paper shortly after the appearance of my preliminary 

 notice in 1897, (Annot. zool. Jap., vol. I. pp. 137140) but various unavoidable circumstances 

 have combined to cause the delay. Meanwhile I have had opportunities of renewing my study 

 on various points and the results here given are different from tliose of tlie preliminary 

 puper in several important respects. 



