98 LOWER VERTEBRATES. 



" After a time it would swim slowly in the tank with no apparent agitation on account 

 of the contact, and come to the surface at the usual intervals to discharge a bubble of 

 air. Having been thus prepared, the fish was permitted to move to and fro at about 

 six inches below the surface, but was prevented from rising. It became uneasy, and, 

 after a few not very violent efforts to disengage itself, emitted a large bubble of air, 

 which rose to the surface. 



"If this emission were all it required, we may suppose that it would have been 

 content. On the contrary, after a second or two of quiet (perhaps resulting from 

 the habit of being satisfied after the respiratory action), the fish became more and 

 more uneasy, moved rapidly to and fro, turned and twisted, and lashed with its tail, 

 and finally escaped from the hand. It rose at once to the surface, and, without 

 emitting any bubble whatever, opened the jaws widely, and apparently gulped in a 

 large quantity of air. It then descended, and remained quiet for the usual interval. 

 This experiment was several times repeated, always with the same result." 



To the physiologist these experiments are highly interesting, for here we see the 

 early stages of the change from an air bladder to the lungs of the higher vertebrates. 

 In the lung-fishes this change of function is carried to a greater extent. The 

 morphologist is also interested in the gradual development of a lung-like organ, and 

 the transference of its duct from the dorsal side of the oesophagus in the fishes to the 

 ventral position which it occupies in the higher vertebrates, including the Dipnoans. 



Tlie bow-fin belongs exclusively in fresh water, preferring the still waters of lakes 

 and sluggish rivers. It ranges from Minnesota south to Florida and Texas. It is very 

 voracious, and eats large numbers of other aquatic animals, but its "flesh is peculiarly 

 soft and pasty, and is of no value for food." Its eggs are moderate in size, and are 

 enveloped in an outer covering, which in structure is much like that found in X,epi- 

 dosteus. Nothing is known of the development, and the students in the interior of 

 our country have here a fine chance to do good work. 



The fossil genera Nbtmus and Amiopsis, of the tertiary rocks, are closely allied to 

 Amia. Frequently associated with this genus are the fossil families Leptolepidse, 

 Caturidffi, and Platyuridse, but these may possibly belong near the salmons and 

 clupeoids, and may be the oldest physostomous fishes. They appear in rocks of the 

 Jurassic age, and appear to have held their position here through a dictum of Agassiz, 

 that any fish from a formation older than the cretaceous must be a ganoid. 



In conclusion, we may say that the group of ganoids appears to be an artificial one, 

 and will probably be divided up (this has been done by some, notably Professor Cope), 

 some of its members being accorded a distinct rank, ^vhile others may be placed among 

 the forms here treated of as teleosts. This will probably be the case with the Lepi- 

 dotidae, which on many accounts appear to belong to the Isospondyli, and to be primi- 

 tive forms of clupeoid and salmonoid fishes. Pterichthys, again, is a problematical 

 form, and probably has nothing to do with the group with which it is usually associated, 

 but may be, according to Professor Cope, either a modified ascidian related to Chely- 

 osoma, or is one of the Acrania directly descended from such a type. 



J. S. KiNGSLET. 



Sub-Class II. — Teleostei. 



Next after the ganoids come the vast majority of living fishes. It is generally 

 admitted that the gradation of the ganoids into the teleostean hosts is evident, and 



