THE OPEN SEA 101 



cradle made by the female only. Moreover, 

 the delicate cradle is made as a secretion from 

 two of the "arms," not as a secretion from the 

 "mantle," the fold of skin which manufactures 

 the shell of all other Molluscs. 



Another pretty case is the egg-raft of the 

 mollusc called lanthina. This open-sea Gas- 

 teropod has a lightly built shell of a fine violet 

 colour, and when the time for egg-laying comes 

 a bubbly float is made in which the eggs are 

 embedded, and this is towed about by the 

 parent as it swims. 



THE OPEN SEA AS A NURSERY 



Another big fact must be included in our 

 picture of the open sea that it is the nursery 

 for the young stages of many shore-animals. 

 Delicate young stages which could not survive 

 for an hour in the rough-and-tumble conditions 

 of the shore are nurtured safely in the spacious- 

 ness and easy-going uniformity of the open sea. 

 There is no better example than the common 

 Shore- Crab (Carcinus mcenas). The develop- 

 ing e gg s ar e carried about by the mother under 

 the shelter of her tail. Out of the eggs come 

 dainty pinhead-like, free-swimming larvae, called 



