Mr George Brook on the Aeration of Marine Aquaria. 381 



diameter in the posterior, tlieir secreting portion, and are 

 twisted back npon themselves. 



The malpighians in G. longicornis much resemble those of 

 LithoUus. In Himantarium Gahrielis there is no increase in 

 their diameter near the opening. 



I hope at an early date to communicate a description of 

 the morphology of the digestive system in other chilopods 

 and in the Chilognatha. 



XXXI. On the Aeration of Marine Aqitaria. By George 

 Brook, Esq., F.L.S., etc. [Plates XVIIL, XIX.] 



(Read 18th February 1885.) 



In carrying on any investigations into the life history and 

 habits of marine animals, success is greatly dependent on a 

 close imitation of the natural conditions of existence. In 

 some respects this is not difficult, and, besides, marine as well 

 as other animals possess in a variable degree an adaptive 

 faculty which enables them to accommodate themselves to 

 new surroundings. We should always bear in mind, how- 

 ever, that these new surroundings are not the natural ones, 

 and that our results obtained in a laboratory may often be 

 influenced by conditions not to be found in a state of nature. 

 Perhaps the most difficult natural condition to imitate, and 

 one which affects all marine animals alike, is a proper aeration 

 of the water. Within the limits of a laboratory tank it is not 

 practicable to aerate the water in a natural way. The 

 oxygenating influence of winds, waves, and tides can take 

 only a very limited share in this work, and we have no scope 

 for the distribating influence of currents. Naturalists have 

 therefore had to take advantage of other methods of keeping 

 the water pure and charged with oxygen. Two distinct 

 methods have been tried on a large scale with varying 

 degrees of success.^ On the first plan the oxygen was 



^ I do not propose to deal here with those small still-water aquaria, in 

 which advantage is taken of the mutual dependence of animal and vegetable 

 life for a proper aeration of the water. 



