254 THE FOOD OF ANIMALS 



this up and moulding it into small rounded portions forming con- 

 venient mouthfuls. 



Many apparently omnivorous forms are found among the 

 Lower Crustacea (Entomostraca), of which the Barnacles pre- 

 sent a very interesting arrangement by which food is secured. 

 Here are included the stalked Ship- Barnacle [Lepas) (fig. 465), 



and the stalkless Acorn- Barnacle 

 {Balanus). Innumerable individuals 

 of the latter roughen the rocks on 

 many parts of the British coasts. 

 In either case the plan of structure 

 is the same (see vol. i, pp. 417- 

 419), and a rough idea is conveyed 

 by Huxley's simile of a man lying 

 on his back with head fixed to some 

 firm object, and getting a living by 

 kicking food into his mouth. But 

 the barnacle is better off than a 

 Fig. 463.-shipBar„aciJ(z.>a. .«./,/..») ^an in Tespect to_ limbs, possessing, 



as it does, six pairs of long slender 

 appendages, which have been compared to tendrils, and are beset 

 with numerous bristles. If one of these animals is placed in a 

 vessel of sea- water the feeding process may be easily observed, and 

 furnishes a curious and interesting sight. First of all the shell 

 opens, and then the slender " legs " are rapidly thrust out, and 

 as rapidly withdrawn with a scooping action, acting, as it were, 

 like a sweep-net, which brings innumerable minute organisms 

 and nutritive particles within reach of the mouth. 



Both salt and fresh water are tenanted by innumerable hosts 

 of minute free -swimming creatures, among which the lowly 

 Crustacea known as Copepods swarm in myriads. A fresh- 

 water type, Cyclops, has elsewhere been described in detail 

 (see vol. i, p. 420). The shape of the body has been likened 

 to half a split pear, the curved side being dorsal and the flat 

 side ventral. From the broad head -end project two pairs of 

 well-developed feelers which row the animal along, and at the 

 same time are no doubt the chief agents by which the presence 

 of food is detected. The mouth is placed a little way back on 

 the under surface, and is provided with four pairs of jaw-like 

 limbs capable of dealing with minute animals and plants, to say 



