CHAPTER XII 



The Reproduction and Growth of Shore Animals 



To a certain extent the eggs and larvae of shore animals 

 are exposed to the same dangers as those which beset the 

 adults. There is this difference, however, to be borne in 

 mind, that inasmuch as the larvae of most shore animals, 

 and often the eggs themselves, are pelagic organisms, they 

 become for a period exempt from the influence of factors 

 normally associated with shore life. Reproduction on the 

 shore thus involves the double problem as to how the young 

 animal is to be launched, and how, later on, if the larva 

 is pelagic, it can obtain a footing in an environment similar 

 to that of its parents ? Speaking generally, the chief risks 

 which beset the eggs and larvae of shore animals may be 

 enumerated as follows : (a) stranding on the shore or being 

 swept out to sea (eggs and larvae) ; (b) desiccation at low 

 tide (eggs) ; (c) varying character of the environment : 

 tides, fluctuating temperature, etc. ; {d) predaceous animals 

 (eggs and larvae) ; (e) failure to obtain a foothold (larvae). 



Adhesive Spawn — Protective Coverings. — So far as the 

 eggs are concerned, the danger of stranding is frequently 

 avoided by the firm way in which they are attached to rocks, 

 weeds, stones, empty molluscan shells, etc. Frequently, 

 the spawn is deposited in flat, adhesive masses surrounded by 

 gelatinous material {e.g. Nudibranchs). Or the embryos 

 may be surrounded by a stout, horny capsule which is 

 attached by a stalk (viz. many Gasteropods). The ova of 

 many Polychaet worms {e.g. Phyllodoce) are enclosed in 

 globular gelatinous envelopes which are moored by a long 

 strand of mucus (see Fig, i8). 



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