Microscopical Essays. 409 



placed them be turned from it, they will be found the next day 

 to have removed themfelves to the fide that is next the light, and 

 the dark fide will be quite depopulated. 



Of the Food of the Hydr^:, and their Method of 

 seizing and swallowing their prey. 



As the hydra fufca, Fig. 7, PI. XXL has the longed arms, it's 

 manner of feeding, and the different manoeuvres it makes ufe of to 

 feize and manage it's prey, are more remarkable than thofe of the 

 two other fpecies ; it will be, therefore, this kind only which will be 

 principally fpoken of under the prefent head. To view them 

 properly, they mould be placed in a glafs feven or eight inches 

 deep. If the polype is fixed near the top of the glafs, their arms 

 for the moft part hang down towards the bottom. This is a very 

 convenient fituation for giving them their food, and to obferve 

 how they manage it. 



An hungry polype fpreads it's arms as - a fifherman his nets; 

 it extends them every way, fo that they form a circle of consider- 

 able extent, every part of which is entirely within the reach of 

 one of them; in this expanded pofture it lies in expectation of 

 it's food ; whatever comes within the verge of this circle is feized 

 by one or another of it's arms. The arms are then contracted till 

 the prey is brought to the mouth, when it is foon devoured. 

 While the arms are contracting, and exerted vigorouffy, (to 

 counteract the efforts the animal which it has feized makes in 

 order to efcape) they may be obferved to fwell like the mufcles of 

 the human body when they are in a flate of exertion. 



The 



