October 11. 1901.] 



SCIENCE. 



565 



cease to be such when the facts necessary 

 to understand them are at our hand. 



DISTRIBUTING MAEINE FISHES. 



The distribution of marine fishes must be 

 indicated in a difi'erent way from that of 

 the fresh- water forms. The barriers which 

 limit their range furnish also their means 

 of dispersion. In some cases proximity 

 overbalances the influence of temperature ; 

 with other forms, questions of temperature 

 are all-important. 



PELAGIC FISHES. 



Before consideration of the coast lines, 

 we may glance at the differences in vertical 

 distribution. Many species, especially those 

 in groups allied to the mackerel family, 

 are pelagic — that is, inhabiting the open 

 sea, and ranging widely within limits of 

 temperature. In this series, some species 

 are practically cosmopolitan. In other cases 

 the genera are so. Each school or group 

 of individuals has its breeding place, and 

 from the isolation of breeding districts new 

 species may be conceived to arise. The 

 pelagic types have reached a species of 

 equilibrium in distribution. Each type 

 may be found where suitable conditions ex- 

 ist, and the distribution of species throws 

 little light on questions of distribution of 

 shore fishes. Yet, among these species are 

 all degrees of localization. The pelagic fishes 

 shade into the shore fishes on the one hand 

 and into the deep-sea fishes on the other. 



BASSALIAN FISHES. 



The vast group of bassalian or deep-sea 

 fishes includes those forms which live be- 

 low the line of adequate light. These, too, 

 are localized in their distribution, and to a 

 much greater extent than was formerly sup- 

 posed. Yet, as they dwell below the influ- 

 ence of the sun's rays, zones and surface 

 temperatures are nearly alike to them, and 

 the same forms may be found in the arctic 

 or under the equator. Their differences in 

 •distribution are largely vertical, some liv- 



ing at greater depths than others, and they 

 shade off" by degrees from bathybial into 

 semi-bathybial, and finally into ordinary 

 pelagic and ordinary shore types. 



The fishes of the great depths are soft in 

 substance, some of them blind, some of 

 them with very large eyes, all black in 

 color, and very many are provided with 

 luminous spots or areas. A large body of 

 species of fishes are semi-bathybial, inhabit- 

 ing depths of 200 or 300 fathoms, showing 

 many of the characters of shore fishes, but 

 far more widely distributed. Many of the 

 remarkable cases of wide distribution of 

 type belong to this class. At such depths, 

 red colors are almost universal, correspond- 

 ing to the zone of red algae, and the colors 

 in both cases are perhaps determined from 

 the fact that the red rays of light are the 

 least refrangible. 



A certain number of species are both 

 marine and fresh water, inhabiting estuaries 

 and brackish waters, while some more 

 strictly marine ascend the rivers to spawn. 

 In none of these cases can any hard and fast 

 line be drawn, and some groups which are 

 shore fishes of one region will be repre- 

 sented by semi-bathybial or fluviatile forms 

 in another.* 



LITTORAL FISHES. 



The shore flshes are in general the most 

 highly specialized in their respective groups, 

 because exposed to the greatest variety of 

 selecting conditions and of competition. 

 Their distribution in space is more definite 

 than that of the pelagic and bassalian 

 types, and they may be more definitely as- 

 signed to geographical areas. 



* The dragonets, CalUonymus, are shore fishes of 

 the shallowest waters in Europe and Asia, hut in- 

 habit considerable depths in tropical America. The 

 sea-robins {Prionotus) are shore fishes in Massa- 

 chusetts, semi-bathybial fishes at Panama. Often, 

 arctic shore fishes become semi-bathybial in the tem- 

 perate zone, living in water of a given temperature. 

 A long period of cold weather will sometimes bring 

 such to the surface. 



