28o THE BIOLOGY OF THE SEA-SHORE 



to stones, where they are accompanied by one of the parents, 

 or, according to Day, to the upper surface of small caverns 

 in the rock. The frequent occurrence of the Nudibranch 

 Calma glaucoides in the neighbourhood of the eggs of goby 

 and shanny has already been remarked. 



The Five-bearded Rockling, Motella mustela, is excep- 

 tional among shore fishes, inasmuch as its eggs are pelagic. 

 This is all the more surprising since the adults are typically 

 tidal forms and seldom, according to M'Intosh (1901, 

 loc. cit.), extend far seaward. Though the eggs are numerous, 

 the adults only occur sparingly among rock pools, so that it 

 is difficult to say which of the two methods, the deposit of a 

 restricted number of demersal eggs which are carefully 

 watched, or the random liberation of large numbers of pelagic 

 eggs, is the more advantageous to the species. Certainly 

 the former method is much the more common in the littoral 

 area. 



Retrospect. — The main facts which emerge from the 

 foregoing survey are as follows : 



(a) The spawn of shore forms is frequently attached 

 and protected by some form of horny or gelatinous invest- 

 ment. 



(b) There is a tendency to modify chapters of the normal 

 life-history in response to special needs. For instance, the 

 larval period of a form living near high-tide mark may be 

 much condensed as compared with that of an allied species 

 living in the Laminarian zone. Cases in point are those of 

 Littorina neritoides and L. littorea. On the other hand, 

 circumstances may sometimes result in the larval stages 

 being prolonged. 



{c) The period of reproductive activity is frequently 

 adjusted to the seasons or may even coincide with a particular 

 phase of the moon {e.g. Co7tvoluta), the result being to allow 

 the larvae the optimum chance of survival. 



(d) Cases of parental care are not uncommon and make 

 economised reproduction possible, in contrast to the great 

 fecundity required in those cases in which the eggs are 

 liberated at random. From a habit such as that of the 



