CYPRINIFORMES 369 



In conclusion, it must be remembered that, in all Gnathostomes 

 except perhaps the Teleostei, the relative position of the organs in 

 question when enumerated from the middle line outwards is as 

 follows : the genital ridge near the base of the mesentery, the meso- 

 nephric ridge with the peritoneal funnels, then the Miillerian duct 

 (Fig.. 55). When the latter develops as a closing groove it is in that 

 position. Now in the Chondrostei there are short open-mouthed 

 ducts, leading behind into the base of the mesonephric ducts ; these 

 oviducts appear to be genuine Miillerian ducts. The short wide- 

 mouthed oviducts of the Salmonidae and the pores of the Anguil- 

 liformes are probably of the same nature (Fig. 355). At all events, 

 no other representatives of the Miillerian ducts can be found in these 

 fish. We may suppose, then, that in Polypterus, Lepidosteus, and most 

 Teleosts the Miillerian groove (developing duct) has shifted to the 

 base of the ovary, so as to occupy the same place as the male 

 collecting duct of the testis ; or that the short Miillerian duct has 

 combined with the homologue of the testicular duct in front, thus 

 forming the parovarial portion of the oviduct, which remains open 

 in Polypterus and closes in Lepidosteus and the majority of the 

 Teleostei. This latter view seems the more probable (Fig. 355). 1 



To classify the Teleostei according to a phylogenetic scheme is 

 a very difficult matter. The more highly specialised forms fall into 

 groups which are fairly well defined, but the position of less 

 differentiated families is not yet well determined owing to lack of 

 palaeontological evidence. If we were to attempt the reconstruc- 

 tion of a primitive Teleost ancestral to all living forms, we should 

 have to attribute to it the following characters : a skull with typical 

 superficial covering bones, with no interorbital septum, with a 

 median gular plate ; a mesocoracoid ; a homocercal tail ; one dorsal 

 and one anal fin ; a spiral valve ; a conus provided with two rows 

 of valves ; cycloid scales and superficial denticles. 2 



No living fish is known to combine these characters, though, 

 except the last, all appear scattered among certain members of the 

 lowest division of the Teleostei as given in modern classifications 

 the Isospondyli (Cope, A. S. Wood ward), Malacopterygii (Boulenger), 

 or Clupeiformes (p. 386). This sub-order represents not a well- 

 defined branch, but at most an assemblage of divergent families, 

 from some one or more of which the other more specialised families* 

 may have arisen. Further, if, following A. S. Woodward, we. 

 include with them the Pholidophoridae and their immediate allies, 



1 We cannot hope to reach a definite conclusion on this difficult subject until the 

 development of the ducts in such forms as Osmerus, Amia, Acipenser, and the Dipnoi 

 has been made known. 



' 2 It is, of course, possible that the denticles on the surface of the body of the 

 Siluridae have been, so to speak, reacquired ; the bony plates on which they rest seem 

 to be secondary, since they often overlie the normal bones of the skull. 



