172 



THE BOOK OF NATURE STUDY 



The struggle for existence seems to be keen in the shore area, 

 and some of the illustrations of it are striking. The dog-whelk 

 (Purpura lapillus) lays 

 its eggs in neatly 

 shaped vases, at first 

 pinkish, afterwards 

 straw coloured, which 



are found abundantly A^-^^L. "^ ^. M >aw n 



in spring on the ledges 

 of the low- tide rocks. 

 Inside these vases 

 a strange infantile 

 struggle occurs 

 " cannibalism in the 



FIG. 85. The empty shell of 



the dog-whelk (Purpura FIG. 86. The common buckle (Buccinum tmdatuni}. The 



lapillus\ a carnivorous 

 gasteropod, abundant on the 

 shore rocks. Beneath is a 

 cluster of its vase-like egg 

 capsules which are attached 

 to the rocks, often to the 

 under side of ledges. 



protruded head shows the mouth (M), the horns (H), 

 and the eyes (E). Protruding from the notch at the 

 mouth of the shell which is a mark of carnivorous 

 gastropods is the respiratory tube or siphon through 

 which water enters and leaves the gill-chamber. The 

 flat muscular ventral surface on which the animal 

 creeps along is called the " foot " (F). It bears posteriorly 

 a flexible lid or operculum, which closes the shell when 

 the animal retracts itself (O). Below the animal is a 

 small cluster of its chaffy egg-capsules, which it attaches 

 to rocks and stones in the Laminarian zone. 



cradle/* for some em- 

 bryos eat their neigh- 

 bours till only an elect 

 few are left. The same story is true of the embryos inside the 

 larger egg-cases of the buckie (Buccinum undatum) and of the great 

 whelk (Fusus antiquus), which are fixed to rocks at a lower level, 



