REPRODUCTION AND GROWTH 257 



Any damage to the nest is at once repaired. If compelled to 

 retreat by the falling tide the fish returns as soon as the way is 

 open. 



Another interesting nesting form is the so-called " kelp- 

 fish " {Heterotrichus rostrata), occurring among the great 

 kelp beds of the shores of S. Carolina, the nest of which has 

 been described by Holder ( 1 907) . The fish usually resembles 

 very closely the seaweed on which it lives, except during the 

 breeding season, when the colour of the male becomes much 

 more vivid. A female, in captivity, was seen to examine a 

 bunch of seaweed, pushing her way through it, and passing 

 many times round it, depositing as she went a pure white 

 viscid cord, which clung to the branches and on which were 

 many small white eggs. Then, while the female rested, her 

 mate mounted guard. The whole nest took two hours to 

 complete and formed a globular white mass about the size 

 of a hen's egg. 



We will now go on to consider the breeding habits of some 

 of the commoner shore species, beginning with sponges and 

 taking each of the more familiar groups in turn. Before 

 doing so, however, it is necessary to emphasise the many 

 gaps in our knowledge of the reproductive habits of even the 

 commonest shore species. Notwithstanding, for instance, 

 the multitude of Polychaets occurring on the shore, it is 

 only in very few cases that the spawn of these forms, even 

 when quite conspicuous, has been identified with certainty. 

 Again, it is only recently (1920) that Tattersall has cleared 

 up a long-standing mistake with regard to the spawning of 

 the common periwinkle {Littorina littorea), showing that 

 the eggs of this species have long been confounded with 

 those of L. obtiisata. Orton has obtained valuable data 

 on the growth rate of a number of marine invertebrates 

 by means of immersing various objects in the sea 

 and subsequently observing and collecting the various 

 kinds of animals growing on them, but it is evident that 

 this is an aspect of shore life which should well repay 

 further study. 



