706 



DIRECTIONS FOR COLLECTING. 



observations with regard to their relation to their host as well 

 as to their early life will prove to be valuable ; nothing is known 

 of the propagation of fishes even so common as Echeneis and 

 Fierasfer, much less of the parasitic Freshwater Siluroids. 



The temperature of the blood of the larger freshwater and 

 marine species should be exactly measured. 



Many pelagic and deep-sea fishes are provided with peculiar 

 small round organs of a mother-of-pearl colour, distributed in 

 series along the side of the body, especially along the abdomen. 

 Some zoologists consider these organs as accessory eyes, others 

 (and it appears to us with better reason) as luminous organs. 

 They deserve an accurate microscopic examination made on fresh 

 specimens ; and their function should be ascertained from obser- 

 vation of the living fishes, especially also with regard to the 

 question, whether or not the luminosity (if such be their function) 

 is subject to the will of the fish. 



Fig. 32L — Scopelus boops, a pelagic fish, with luminous orgcans. 



