THE OPEN SEA IOI 
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 manu- 
factures the shell of all other Molluscs. 
Another pretty case is the egg-raft of the 
mollusc called Ianthina. 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 condi- 
tions of the shore are nurtured safely in the 
spaciousness and easy-going uniformity of the 
opensea. There is no better example than the 
common Shore-Crab (Carcinus menas). The 
developing eggs are carried about by the 
mother under the shelter of her tail. Out of 
the eggs come dainty pinhead-like, free-swim- 
