122 



INTRODUCTION TO ZOOLOGY 



They are laid in little horny capsules, which are fused together 

 in a sponge-like mass, often in clusters of a hundred or more. 



Each capsule contains 500 to 600 

 eggs, but only a small number of 

 these develop. The eggs are laid 

 in the autumn, but the little larvae 

 do not leave the egg-case until the 

 spring. They are able at first to 

 swim freely in the water. 



Nasm reticulata, the 

 lls^^^. Dos Whelk, may be 



Fig. 76. — Buccinum undutum. 

 A small Cluster of Egg Cap- 

 sules. 



may 

 low tide 



Dog 



found near 



mark crawling over the rocks or sand at the bottom of the 

 water, or completely buried in the sand except for its waving 



Fig. 77.^The Dog Whelk (Nassa reticulata). 



A, Crawling over the bottom of a rock pool ; B, at rest, partly buried in the sand ; 

 E, eggs attached to a stalk of seaweed. 



respiratory 

 black, and 

 broad front 



Cypraea. 

 The Cowry. 



distance up 

 The Murex. 



siphon. The broad yellow foot is speckled with 

 has a small horn-like process on each side of its 

 end and two small pointed "tails" at the back end. 



The Cowry is another carnivorous gill-breath- 

 ing marine snail, the shell of which is very 

 thick and hard ; the mantle is reflected for some 

 each side of the shell (Fig. 78). 



The genus Murex is interesting because of the 

 Spiny Murex, the Mediterranean species, from the 



