426 ANIMAL LIFE-HISTORIES 



large form, as it may be as much as 2 feet long, and development 

 is entirely internal. A single brood consists of from 50 to 100 

 individuals, each about ij inch in length and resembling the 

 adult in shape. The comparatively small size of the family is 

 correlated with the protective nature of the development, which 

 gives the young fishes a much better chance than usual of attain- 

 ing maturity. 



The fresh waters of the land are largely tenanted by forms 

 which have been driven to take refuge there, as a result of the 

 keen struggle for existence which is always going on in the sea. 

 And some marine fishes increase the chance of survival of their 

 species by using rivers as their nurseries. This has already been 

 illustrated in the case of certain Lampreys (see p. 423), and the 

 Salmon (Salmo salar) is a well-known instance of the same thing. 

 These fishes periodically migrate into fresh water for the purpose 

 of spawning, and they excavate by means of the tail a sort of 

 trench in which the eggs are deposited, afterwards being covered 

 by sand or gravel. 



The parental duties of Fishes usually terminate when the 

 eggs have been laid, but to this there are some interesting excep- 

 tions both among marine and freshwater species. One instance 

 is afforded by the Butter-Fish or Gunnel (Centronotus Gunnellus), 

 a slimy and rather eel-like Blenny, often to be found in the rock- 

 pools of our coasts. Cunningham (in Marketable Marine Fishes) 

 speaks as follows of it in this connection: " At St. Andrews Mr. 

 Holt saw the spawning of the Butter- Fish or Gunnel in the 

 aquarium in February. The eggs were adhesive, and the parents 

 were seen to roll the mass of eggs into a ball by coiling their 

 bodies round them, not both parents together, but the male and 

 female in turns. It has been observed by Professor M'Intosh and 

 Mr. Anderson Smith, that in the natural condition the parents are 

 found coiled round the balls of spawn, which are somewhat larger 

 than walnuts and not attached to anything." Female Fishes are 

 not remarkable for any great display of solicitude as regards their 

 offspring, but some honourable exceptions, besides that of the 

 Butter- Fish, have been recorded. In a form (Aspredo) native to 

 Guiana, and belonging to the widely distributed freshwater family 

 of Cat- Fishes (SiluridUe), the under side of the female's body 

 becomes rough and spongy at the time of spawning. After the 

 eggs are laid she presses against them, so that they adhere to this 



