REPRODUCTION AND GROWTH 255 



parental care on the part of shore fishes are on the same Hnes. 

 In all there is the evidence of some powerful stimulus 

 operating on the parent to keep it in touch with the 

 eggs. 



As to how far the presence of the parent is operative in 

 warding off enemies it is not always easy to pronounce. 

 Probably in most cases the habit is concerned rather with the 

 necessity for keeping the eggs aerated than with active 

 protection. The male lumpsucker, for instance, has been 

 observed to keep up a continual motion of the pectoral 

 fins and so maintain a steady flow of water about the eggs, 

 which are laid in such large masses that, without this atten- 

 tion, the central ones might, in still water, easily be asphyxi- 

 ated. Against this, however, we may place the case of the 

 stickleback which shows itself very active in defence of the 

 eggs, and will boldly attack any intruder however much 

 stronger than itself. 



Nest-building. — The habit of nest-building found in the 

 fresh-water stickleback and its marine relative the fifteen- 

 spined form as well as in other less familiar shore fishes, 

 evidently represents an elaboration of the habits described 

 above. According to Couch (1877), the nests of the fifteen- 

 spined stickleback are placed in sheltered situations where 

 there is ample circulation of pure water without violent 

 wave action. The nests may occur hanging in rock pools 

 and not infrequently between tide-marks where the moisture 

 of the materials is apparently sufficient to protect the grains 

 of spawn from drought. While sometimes making use of 

 the materials found growing on the spot selected, the fish 

 has also been observed to collect some of the softer kinds 

 of green or red seaweeds and to join them together with so 

 much of the coralline tufts growing on the rocks as will 

 afford firmness to the structure and constitute a pear-shaped 

 mass five or six inches long, about the size of a man's fist. 

 The whole structure is held together by a network of threads 

 formed of mucus secreted by the fish, and there is evidence 

 of considerable skill in the way in which these threads are 

 interwoven through^the weeds (see Fig. 16). After the ova, 



