DRIFTING LIFE 133 



lobster that is most eaten for food in the British Isles. It 

 is the " Langouste," which is, however, much preferred as 

 a delicacy by the French. 



The larva is a most curious sight (Plate 51). The body, 

 measuring about a quarter of an inch across in the oldest 

 individuals, is quite transparent and flattened like a piece 

 of paper, while the long feathery legs and projecting eyes 

 stick out all round and effectively aid the purpose of the 

 flattened body in preventing the animal from sinking 

 through the water. 



It is not necessary to resort to experiment to prove that 

 these structures are an aid to suspension in the water. It 

 is known that the viscosity of water varies with the tem- 

 perature, a rise in temperature lowering the viscosity to a 

 marked degree, so that the resistance the water offers to a 

 body sinking in it is considerably lessened. If, then, an 

 animal or plant lives normally in warm water it will need 

 to be extra well equipped with hairs and spines compared 

 with its cousins who live in cold waters. 



Now, it is a remarkable fact that by the side of organisms 

 from cold and temperate regions those from the tropics 

 exhibit to a much greater degree these structural excres- 

 cences, making many of them bizarre and grotesque in 

 appearance. It has even been found that the same species 

 of Peridinian may differ from place to place in form. For 

 instance, in two individuals of the same species, the one 

 from tropical seas has very much longer horns than those 

 of its relative from our own colder waters. 



In these few pages an attempt has been made to put 

 before the reader some of the main features of that remark- 

 able community of drifting life, the plankton. Their im- 

 portance cannot be over-estimated and plankton study 



