STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 817 



comes off a convoluted tube (pr.n.}, forming the main mass of 

 the pronephros, and ending in the segmental duct (sd.\ 



FIG. 



Diagrammatic views of the pronephros of Lepidostetis. 



A, pronephros supposed to be isolated and seen from the side ; B, section through 

 the vesicle of the pronephros and the ciliated peritoneal funnel leading into it ; 

 pr.n., coiled tube of pronephros; s</., segmental or archinephric duct ; /, peri- 

 toneal funnel ; v., vesicle of pronephros ; &v., blood vessel of glomerulus ; 

 /., glomerulus. 



The different parts do not, however, appear to have the same 

 morphological significance as those in the mesonephros. 



Judging from the analogy of Teleostei, the embryonic structure 

 of whose pronephros is strikingly similar to that of Lepidosteus, 

 the two pronephric chambers into which the segmental ducts 

 open are constricted off sections of the body-cavity. 



