EGGS AND LARV^ AND THEIR DEVELOPMENT 



91 



these cases undertakes the duties of a nurse. The male gobies 

 make a home for the eggs, it can scarcely be called a nest, and 

 remain in it until the eggs are hatched. The common sand goby 

 when about to become a father scoops out 

 the sand from beneath an empty shell, usually 

 that of a Pecteii (commonly called clam, or 

 scallop), and invites females to lay their eggs 

 in the domicile thus simply prepared. The 

 female deposits her eggs on the lower surface 

 of the shell, which forms the ceiling of the 

 nursery, and the male remains on guard. 

 The action of his pectoral fins is necessary 

 for the well-being of the eggs, for without 

 their movement the eggs would die of suf- 

 focation. The object of the father's exertions 

 is therefore chiefly to secure aquatic ventila- 

 tion of the cavity in which his progeny are 

 developing. The butter-fishes or gunnels, 

 common shore fishes belonging to the blenny 

 family, roll the eggs into a ball after they are 

 laid by coiling their bodies round the mass, 

 the male and female taking possession of the 

 eggs alternately. Fig. 43 is from a sketch of 

 one of these fishes with a mass of eggs as 

 observed in the St. Andrews Laboratory by 

 Mr. Holt. The parents remain with the eggs until they are 

 hatched. 



The large lump-sucker {Cjcloptents hiuipus) is another species 

 in which the male keeps guard over the eggs and keeps up an 

 artificial flow of water over and through the mass of spawn, 

 which is attached to rocks, posts, or piles in the water. There 

 are also fishes which are true nest-builders. The commonest 

 instances of this are afforded by the sticklebacks {Gasterosteus and 

 SpinacJiia). Two species live in fresh water, the three-spined 

 and the ten-spined, but the larger fifteen-spined species occurs 

 in the sea near shore, and in the brackish waters of estuaries. 

 According to Buckland's descriptions the nest of the fresh-water 

 forms is made of fibrous materials resting on the ground, with a 

 hole in the top, and the male fish frequently places himself 

 above the nest with his snout towards the opening, fanning the 



Fig. 42. — Egg of a 

 species of Goby, 

 from lower side ot 

 stone on shore at 

 Falmouth. 



