CHARACTERISTICS AN T D HABITS OF FISHES 35 



nests and care for their young, often carrying them in 

 their mouths. Certain kinds of dog fish and angel fish 

 keep their young inside their oviducts until they are 

 completely formed. The only notable example of a 

 fish common to British waters that exercises parental 

 care is the stickleback. Spawn is deposited by a number 

 of different females in a nest constructed of stones 

 and weed, and is guarded by a male until all the eggs 

 are hatched. 



The eggs of the Crustacea, for example the lobster, are 

 found attached in large numbers to the swimmerets 

 feathery processes that are situated underneath the 

 tail. When in this condition, the lobster is known as 

 " berried," and, if captured, should be returned to the 

 sea. The eggs are sticky and are laid while the lobster 

 lies on her back, and so become attached to the hairs 

 of these feathery processes. Berried crabs, prawns and 

 shrimps may also be observed on the seashore in the 

 spring and early summer. 



The mollusca, e.g. mussels, periwinkles, oysters, 

 deposit their eggs in the sea-water. The eggs float to 

 the surface, hatch out, and drift about with the other 

 constituents of the plankton. The fully developed 

 larvae fall to the sea bottom and become attached to 

 seaweed and stones. 



The period of incubation of fish eggs varies according 

 to the species of fish, and for the same species is pro- 

 longed by a low temperature. Plaice eggs, fertilized in 

 January, hatched in eighteen days ; others, fertilized in 

 April, were hatched in nine days. 



Ah 1 fish, on emerging from the egg, enter upon a larval 

 stage in which they resemble each other very closely 

 (see Fig. 1). (Thus, the larvae of plaice are quite 

 symmetrical, like those of the cod or other round fish.) 

 The newly hatched larvae drift helpless in the water for 



