164 SUB-CLASS GANOIDEI. 



Hyoid gill, but no pseudob ranch or 



spiracle Sca'phirhynchus. 



Hyoid gill absent, pseudobranch and 



spiracle present Polyodon 



{Spatularia). 



Hyoid gill and pseudobranch absent, 



spiracle present Polypterus. 



Hyoid gill absent ; pseudobranch and 



spiracle also absent (4 double gills) . Amia. 



In those forms {Polypterus and Polyodon) without hyoid gill 

 the ventral aorta still gives a branch to the hyoid arch. 



Abdominal pores* are present in all living Ganoids. Their 

 external openings are placed on each side of the anus and they 

 open internally into the body cavity. 



Pericardio-peritoneal canals are present in the Sturgeons as 

 single unbranched tubes ; they appear to be absent in other 

 Ganoids. 



Of these characters which on the whole suggest Elasmobranch 

 more than Teleostean affinities, it will be convenient to treat the 

 urinogenital organs more fully at this point. 



The urinogenital organs present many features of interest, 

 and as they differ in important points in the different members 

 of the group it will be necessary to describe them at some length. 

 In all of those, the development of which is known, there is a 

 pronephros in the larva, constructed on the Teleostean type, i.e. 

 it consists of one large malpighian body (Fig. 92, v) connected 

 by a convoluted tube (pr.w) with the anterior end of the longi- 

 tudinal duct {sd) of the future kidney. In Lepidosteus and 

 possibly in others, this body is connected with the peritoneal 

 cavity by a ciliated canal {/). In none of them does the kidney 

 show any differentiation into a meso- and meta-nephros, and 

 in all the oviduct (miillerian) joins the kidney duct of its side 

 posteriorly. Moreover miillerian ducts appear to be in all classes 

 present, generally in both sexes, and they present the peculiarity 

 ot being short and opening into the body cavity at a point much 

 nearer the anus than in other groups in which they are found. 



We have full knowledge of the urinogenital organs in two 



* Bles, " Correlated distribution of Abdominal Pores and Nephro 

 stomes in Fiphes," Journ. Anat. and Phys., 32, 1898, p. 484. 



