FOR COLLECTING. 705 



It is of the greatest importance to note the longitude and 

 latitude at which the objects were collected in the open ocean. 



Fishing in great depths by means of the dredge, can be 

 practised only from vessels specially fitted out for the purpose ; 

 and the success which attended the " Challenger," and North 

 American Deep-sea explorations, has developed Deep-sea fishing 

 into such a speciality that the requisite information can be 

 gathered better by consulting the reports of those expeditions 

 than from a general account, such as could be given in the present 

 work. 



Fishes offer an extraordinary variety with regard to their 

 habits, growth, etc., so that it is impossible to enumerate in 

 detail the points of interest to which the travellers should pay 

 particular attention. However, the following hints may be 

 useful. 



Above all, detailed accounts are desirable of all fishes forming 

 important articles of trade, or capable of becoming more generally 

 useful than they are at present. Therefore, deserving of special 

 attention are the Sturgeons, Gadoids, Thyrsites and Chilodactylus, 

 Salmonoids, Clupeoids. Wherever these fishes are found in 

 sufficient abundance, new sources may be opened to trade. 



Exact observations should be made on the fishes the flesh of 

 which is poisonous either constantly or at certain times and 

 certain localities ; the cause of the poisonous qualities as well as 

 the nature of the poison should be ascertained. Likewise the 

 poison of fishes provided with special poison-organs requires to be 

 experimentally examined, especially with regard to its eff"ects on 

 other fishes and animals generally. 



All observations directed to sex, mode of propagation, and 

 development, will have special interest : thus those relating to 

 secondary sexual characters, hermaphroditism, numeric proportion 

 of the sexes, time of spawning and migration, mode of spawning, 

 construction of nests, care of progeny, change of form during 

 growth, etc. 



If the collector is unable to preserve the largest individuals 

 of a species that may come under his observation he should note 

 at least their measurements. There are but few species of fishes 

 of which the limit of growth is known. 



The history of Parasitic Fishes is almost unknown, and any 



2z 



