520 SUMMARY OF CURRENT RESEARCHES RELATING TO 



3. The Teleostomi are further provided with jointed and branched 

 bony, dermal rays, developed outside the actinotrichia. They bear, in 

 primitive forms, the closest resemblance to the body scales, and Mr. 

 Goodrich proposes to call them " Lepidotrichia" They have doubtless 

 arisen through modification of scales, and in the primitive Teleostomes 

 they often extended into the body by means of a long proximal un- 

 jointed piece passing below the body-scales. 



4. In the Dipnoi are found jointed, branched, dermal rays, of bony 

 substance, containing bone-cells. The name " Camptotrichia " is pro- 

 visionally given to these rays, which appear to be in a degenerate con- 

 dition in the highly modified living forms Lepido siren and Protopterus, 

 and even to some extent in Ceratodus. The camptotrichia are always 

 provided with a proximal unsegmented region, deeply imbedded in the 

 body, and covered by the body-scales. Scales also extend over the 

 whole or the greater part of the fins, overlying the dermal rays. The 

 evidence favours the view that the camptotrichia represent the lepido- 

 trichia of the Teleostomes. 



It may be that lepidotrichia have originated from modified scales, 

 and the camptotrichia of Dipnoi from somewhat degenerate insunk 

 lepidotrichia covered by a secondary extension of the body-scales. But 

 the presence of a proximal joint of considerable length extending below 

 the body-scales in some Teleostomes (such as Cheirolepis) is not easy to 

 account for ; and the relation which the inner ends of the ceratotrichia, 

 camptotrichia and lepidotrichia bear to the muscles, connective tissue, 

 and endo-skeleton, is so similar in all fishes that it is difficult to believe 

 that all these rays have not been, at all events partly, derived from some 

 common form. 



According to the second and alternative theory, it may be supposed 

 that the camptotrichia of the Dipnoi have been derived from the cerato- 

 trichia of the Elasmobranchii, and that they are overlaid with scales as- 

 the horny fin-rays are overlaid with denticles. The jointing of the 

 distal region of the rays would follow on their ossification. On such a 

 view it might be supposed that the lepidotrichia of the Teleostomes have 

 been formed by the fusion of the original dermal rays with the super- 

 ficial scales in the distal region, but not in the proximal region, where 

 the rays were deeply imbedded and remain unjointed. From a com- 

 pound dermal ray so formed the lepidotrichia of the higher Actinopterygii 

 would be derived by the shortening of the proximal piece. The author 

 inclines to the first theory. 



The Physiology of the Swim-Bladder of Fishes.* — A. Jaeger dis- 

 cusses this with particular reference to Thilo's f conclusion that " the 

 air in the swim-bladder is drawn from the atmosphere, swallowed, and 

 brought into the bladder through air-passages." He points out that there 

 is present a mechanism whereby the size of the swim-bladder regulates 

 most exactly the specific gravity of the fish. How, by the simple taking 

 in of air from the mouth such a delicate regulation should have come into 

 existence is not easily seen : indeed, on Thilo's explanation this mechanism 

 is unnecessary. The whole activity of the swim-bladder organs is under 



, * Biol. Centmlbl., xxiv. (1904) p. 129-42. 

 f Op. cit., xxiii. Nos. 14 and 15. 



