MORPHOLOGY OF CYPRIiNODONT FISHES. 23 



It is only by a study of the actual behaviour of these fishes 

 during the breeding-season that one can hope fully to understand 

 the purpose for which this elaborate apparatus has been evolved. 



9. Comparison of the Priapmm ivith other Copulatory 

 Organs of Fishes. 



In many bony fishes a papilla bearing the genital aperture 

 forms a simple but efficient intromittent organ ; in others the 

 anal fin is utilized, the vas deferens either opening at its base or 

 being prolonged on the fin, which may form a copulatory organ 

 of considerable complexity of structure, as in the viviparous 

 Cyprinodonts, Poeciliinse, Anablepinse, etc. TRegan, 10; Gar- 

 man, 1 ; Langer, 4). 



In its asymmetry and in being either dextral or sinistral 

 the priapium agrees with the copulatory organ of Anablep>s 

 (Gar man, 1). 



In the Phallostethinse the remoteness of the genital opening 

 from the anal fin explains why the latter has not been involved, 

 but does not explain the exti-aordinary complexity of the pri- 

 apium, which parallels the mixojDterygia of the Selacliians in its 

 specialized skeletal and muscular system (Jungersen, 3). 



In the mixopterygia new skeletal elements are developed, and 

 may either margin a groove or may become movably articulated 

 with the main axial piece ; one may project as an external spine, 

 in this case formed of calcified cartilage, not of bone. Another 

 parallel with the priapium is that the mixopterygia attain their 

 full development rapidly as the individual becomes sexually 

 mature. 



In the Selachians the mixopterygium has a nearly uniform 

 structure in members of the same family, or even of the same 

 suborder (Huber, 2 ; Regan 7), and the differences between the 

 priapia of Phallostethus and Neostethus are as great as between 

 the mixopterygia of the subclasses Holocephali and Euselachii. 



10. Rank and Position of the Phallostethince. 



There can be little doubt but that Neostethus and Phallostethus 

 belong to the family Oyprinodontidae, and they seem to agree in 

 every way with the most generalized subfamily, the Fundulinse, 

 except for three features of specialization, namely, the anterior 

 position of the anus, the absence of pelvic fins, and the develop- 

 ment of a priapium in the male. This view as to their relation- 

 ship is best expressed by placing them in a distinct subfamily, 

 Phallostethinse, of the Oyprinodontidae, a family that already 

 includes both oviparous and viviparous fishes, the latter with 

 intromittent organs of three difterent types (Regan, 8). 



Other examples of animals which i^etain the general structure 

 of the group to which they belong, whilst one particular organ or 

 system is profoundly modified or some new feature of importance 



