MOLLUSCS 141 



in it, then siphons were present, and the living animal is to be 

 sought in sand, mud or rock. The shells of edible mussel and 

 Tapes show this contrast well. 



The Gasteropods of the shore are very numerous, and include 

 both forms with and those v/ithout shells. Before proceeding 

 to mention a few common and hardy forms we may say some- 

 thing about the spawn, connected with which are many points 

 of great interest. In wandering over the rocks in early spring 

 one may often find curious white structures like ladies' frills, 

 which stand up from the surface of the rock, and consist of a 

 gelatinous matrix in which are lodged innumerable minute eggs. 

 These are the egg ribbons of sea-slugs, species of Doris being 

 common forms. If a little of this spawn be placed in the aquarium, 

 or preferably in a dish by itself, in course of time the minute larvae 

 will hatch out, and are just visible to the naked eye. If the 

 spawn has been placed in a glass vessel, and the water is well 

 oxygenated, it may become absolutely turbid with the tiny 

 larvae, who are free-swimming, not sluggish like the adults, and 

 jerk themselves through the water. In the sea, however, they 

 cannot swim against the currents, and are carried passively 

 about, thus serving as a means of distribution. Look at the 

 pools in which the egg-ribbons naturally occur, and note how 

 vast a number of the larvae must die prematurely by being 

 flung up on the sides of the pool, no less than as the result of the 

 appetite of the many animals who feed on minute forms of life. 

 Endeavour with a lens to make a rough calculation of the number 

 of eggs in each ribbon, or each inch of ribbon, and you will realise 

 that the enormous numbers are necessary because of the waste 

 of larvae. To contrast with this type of spawn take the little 

 vase-shaped capsules of the dog whelk, found attached separately 

 to the rocks, or the great egg masses of the common whelk, both 

 common objects on the shore. In the whelk the capsules are 

 glued together to form great masses, each capsule being of 

 irregular shape and having a tough wrinkled skin. The whole is 

 glued to a stone, and when first laid each capsule contains several 

 hundred eggs. The older capsules are empty and show merely 

 the little hole through which the young whelks made their escape. 

 When they escape they are not, like the larvae of Doris, minute, 



