8 Memoir Sears Foundation for Marine Research 



these dorsal ribs may not be homologous, embryologically, with those of the elasmo- 

 branchs (26: 215-217). 



A spiral valve in the intestine, which is universal in elasmobranchs and chimae- 

 roids, is well developed in the living coelacanths {$0: 426, 2582, Millot and Anthony), 

 in the Dipnoi, and in the polypteroids alone among bony fishes; but it is represented in 

 vestigial form in the acipenserids (sturgeons) and polyodontids (paddlefishes). A struc- 

 ture that more or less suggests the elasmobranch spiral valve has been reported also 

 as occurring in Chirocentrus, an Indo-Pacific genus falling among the clupeoids {18: 

 160, pi. 565; ^5: 116, fig. 77 A, Goodrich), in Argentina silus (the common herring 

 smelt of the North Atlantic),-^ in Salmo gairdneri (rainbow trout), Thyniallus (grayling), 

 and the Coregonidae (whitefishes) among the salmonids (information from Daniel Co- 

 hen), in Macropinna among the Argentinoidea (15: 282), in the young of the characid 

 genus Curinata (information from G. S. Myers), and in Alepocephalus {18: 172, 176). 

 But the so-called spiral valve of these isospondylous fishes probably is not homologous 

 with the spiral valve of elasmobranchs and chimaeroids.^* 



On the males of living cartilaginous fishes among which internal fertilization in 

 the female is universal, a copulatory organ commonly called a clasper is developed in 

 connection with each pelvic fin. But the male copulatory organ of the few bony fishes 

 whose eggs are fertilized internally is single (typically) and has no connection with the 

 pelvic fins, being developed either from the genital papilla on the urogenital orifice, or 

 in connection with the anal fin, or as a special structure on the chest. However, the 

 phallostethids (Indo-Australian freshwater fishes of the Order Percesoces) are an ex- 

 ception, for their "much modified pelvic fins and girdle" join in the formation of the 

 copulatory organ {2: 478). 



Finally, such of the bony fishes as pass their lives in salt water maintain their body 

 fluids in osmotic balance with the surroundings in one way, elasmobranchs in another. 

 In each case it is a problem of maintaining the concentration of salts in the blood at a 

 level lower than that of the surrounding sea water; the osmotic pressure in the body 

 fluids of marine teleosts is only about 40 "/o of that of sea water." Elasmobranchs 

 solve this problem by retaining in their blood and tissues much of their nitrogenous 

 wastes in the form of urea; thus they raise the total concentration of materials in solution 

 to a level that is nearly as high as, or even higher than, that of the surrounding sea water 

 without increasing the salt concentration (74: 393). As a result of this mechanism, the 

 marine sharks and rays have no special need of conserving water. According to Black, 

 "They rarely drink salt water and obtain free water in their food" {l2\ 187). Marine 

 bony fishes, never having chanced on this device, prevent an accumulation of salt-ions 



25. Kendall and Crawford {42: 10, fig. i A) pictured Argentina as having a complete spiral valve, but Cohen writes 

 that while he has noted spiral thickenings in the intestine of various Argentinidae, including six specimens of Ar- 

 gentina silus {16: 121), in none of these last did he "observe a functional spiral valve as figured by Kendall and 

 Crawford." 



26. According to Jacobshagen (9: 611), the structure that has been called by this name among the Isospondyli actu- 

 ally represents a series of simple circular ridge-like thickenings of the inner surface of the intestine. For further 

 discussion, see Cohen {16: 96, 98). 



27. Estimated by Denton and Marshall {21: 754) from data assembled by Krogh {44: 130 ff). 



