COURTSHIP AND NURSERY DUTIES. 115 



the dangers that threaten pelagic and demersal 

 eggs, and need only provide against accidents at 

 the hands, or rather mouths of carnivorous neigh- 

 bours in the immediate Dt-ighbourhood. 



Many marine fishes leave the crowded sea, and 

 its innumerable dangers, to setk safety for their 

 offspring in rivers. Such, for the most part, retain 

 the old pelagic habit of leaving the eggs uncared 

 for, consequently they are produced in large 

 numbers to resist tie inroads made upon their 

 numbers, and upon the young fry, by enemies of 

 all kinds. What these inroads are like we shall 

 show in the next chapter. 



The salmon is one of the best known instances 

 of a marine fish which ascends rivers to deposit 

 the eggs. Considerable care is manifested in the 

 disposal of these. They are laid in a rough sort 

 of nest called a redd. This is trench-like in form, 

 and made by the female, in exactly what way 

 seems uncertain, but apparently by ploughing 

 out the gravel — the soil always chosen for this 

 purpose — with the under surface of her body. 

 The eggs, which are large, are deposited herein a 

 few at a time ; and after having been fertilised 

 by the male, become heavier, and sink to the 

 bottom of the trench. Being somewhat sticky 

 externally they adhere to the bottom, and are 

 then lightly covered over with gravel and left to 

 hatch. The loose gravel soil allows a complete 

 aeration, necessary for the development of the 

 egg. The burying of the egg is a precaution 

 against the raids of birds and other fishes, which 

 greedily devour these exceedingly delicate and 

 nutritious tit-bits. 



