/J,9i;. 



K. 





JUL 11 



TW9 



PISCES TELEOSTEI 



(OSSEOUS FISHES) 



Skeleton complete and. usually, ossified. Olfactory organ double. The optic nerves 

 only decussate, and do not form a chiasma. Only two valves" in the arterial bulb. 



In addition to theii* other characteristics, the com- 

 paratively lax arterial bulb of the two-chambered heart, 

 from which the blood passes to the arteries of the 

 branchial arches, and the simple decussation of the 

 optic nerves, \vhich, at their exit from the brain, only 

 cross each other without fusing together their fibres, 

 place these fishes lower on the scale of development 

 than the Chondrosteans, Chondropterygians and the 

 Ganoids (the latter unrepresented in the Scandinavian 

 Fauna), which orders come nearer the Batrachians. On 

 the other hand, the double olfactory organ, which the 

 osseous fishes possess in common with the above-men- 



tioned higher orders, separates them from the Cyclo- 

 stomes, which are represented in Scandinavia by the 

 lampreys, •while the skull places them as ^vell as all 

 other true iisli, as vertebrates, high above the Cirro- 

 stomes, the sub-class to Avhich the lancelet belongs. 

 Thus, w^hile it is true that the osseous fishes do not 

 occupy the highest rank among fisli with respect to 

 their general degree of development, regarded as fish 

 they are nevertheless, above all the others, distinctly 

 marked by their usually ossified skeleton and the ma- 

 nifold development of their organs to meet the require- 

 ments of aqueous life. 



TELEOSTEI PHYSOCLYSTI 



Osseous fishes with the air-bladder, if present, closed (without pneumatic duct) at least in the adult. 



The air-bladder, which corresponds anatomically, 

 though not physiologically, to the lungs of the higher 

 vertebrate animals, is originallj^ an outgroAvth of the 

 digestive canal, but loses in the most highly developed 

 fishes its immediate connection with this canal. Such 

 a change is in itself a sufficient indication of a more 

 advanced degree of development, and has consequently 



full claim to he regarded in a systematic scheme of 

 arrangement. In certain cases -where the air-bladder 

 is absent — as, for instance, in the common mackerel, 

 whereas it exists in the so called Spanisli mackerel, 

 \\-hich is nevertheless a very closely allied species — 

 we must be guided by other resemblances to assign the 

 fish its place among the Phj-soclysts. 



" Some Clupeoids form an exception, as they retain a rndiment of tin- Ganoid conus arteriosus at the base of tlie bulb. Cf. Bo.\s: 

 Om conus arteriosus lios Butirinus og hos andre Teleostei. Vidensk. Meddcl. Nafurli. For. Kbnhvn 1879 — 80, p. 333. Generally too 

 rudiments are to be found of two more valves in the arterial bulb between the others; but in Orthagoriscus mola (cf. Wellenbergu: Observ. Anat. 

 de Orth. mola, Lugd. Batav. 1840) these rudiments are true valves. 



Scandtnnrinn Fishes. 



