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Nachdruck verboten, 

 üebersetzungsrecht vorbehalten. 



The Development of the Urinogenital Organs 

 of the Lamprey. 



By 

 William Morton Wheeler. 



(From the Zoological Institute of the University of Würzburg.) 



With Plates 1—7. 



Long before the Selachians and Amphibians had become favorite 

 paradigms of development, morphologists turned to the Cyclostomes 

 for a revelation of the fundamental structure of the Vertebrate urino- 

 genital system. These older researches on lampreys and hag-fishes 

 have been of no little importance in shaping existing theories. Thus 

 Johannes Müller's study of the mesonephros of Myxinoids (1845) 

 furnished the foundation of our present conception of the metamerism 

 of the Vertebrate kidneys, and Wilhelm Müller's careful study of 

 the very typical pronephros of the lamprey (1875) was the key to 

 our understanding of that organ in other Craniotes. It was, moreover, 

 Max Schultze's observations on the ciliated pronephric funnels of 

 the lamprey (1856) that suggested to Gegenbaur (1870) the theory 

 of the homology of Verraian and Vertebrate nephridia. 



Since the failure of recent elaborate studies on the pro- and meso- 

 nephroi of Selachians, Amphibians and Teleosts to furnish a solution 

 of many important problems, investigators are again turning their 

 attention to the lowest Craniota, especially to the long-neglected Myxi- 

 noids. Less attention is bestowed on the Petromyzontia , although 

 they are, with the single exception of the Myxinoids, the most primi- 

 tive of all existing Craniotes. 



Zool. Jahrb. SUl. Abth. f. Morph. 2 



