I lO iv. 6 — iv. 8. 



bent inwards, and this never occurs in the anterior limbs.^^ The 

 whole number of legs, including those used in leaping, is six, iri 

 all these insects. 



(Ch. y.) In the Testacea^ the body consists of but few parts, 

 the reason being that these animals lead a stationary life. For 

 such animals as move much about must of necessity have more 

 numerous parts than such as remain quiet ; for, the more diversified 

 the movements, the greater the number of organs required to effect 

 them.2 Some species of Testacea are absolutely motionless, and 

 others very nearly so. They would thus fall an easy prey to their 

 enemies, were it not for the hardness of the shell with which 

 nature has invested their body as a means of protection. This 

 shell, as already has been said, may have one valve, or two 

 valves, or be turbinated. In the latter case it may either be 

 spiral as in whelks, or merely globular, as in the Echini.^ When 

 it has two valves, these may be gaping, as in scallops and 

 mussels, where the valves are united together on one side only, 

 so as to open and shut on the other, or they may be united 

 together on both sides, as in razor-fishes,* In all cases alike 

 these Testacea have, like plants, their head downwards. The 

 reason for. this is that they imbibe their nourishment from below, 

 just as dok plants with their roots.^ Thus the under parts come 

 in them to be above, and the upper parts to be below. The body 

 is enclosed in a membrane, and through this the animal filters 

 suitable fluid and absorbs nutriment. In all there is a head;^ but 

 none of the other parts, excepting the receptacle for food, has any 

 distinctive name. 



(Ch. Z.) All the Crustacea ^ can crawl as well as swim, and 

 accordingly they are provided with numerous feet. There are 

 four main genera, viz. the Carabi, as they are called, the Astaci, 

 the Carides, and the Carcini. In each of these genera, again, 

 there are numerous species, which differ from each other not only 

 as regards shape, but also very considerably as regards size. For, 

 while in some species the individuals are large, in others they 

 are excessively minute. The Carcinoid and Caraboid Crustacea 

 resemble each other in possessing claws. These claws are not 

 for locomotion, but to serve as hands for seizing and holding 

 objects ; and they are therefore bent in exactly the opposite 

 direction to the feet, being so twi-sted as to turn their convexity 

 towards the body, while the feet turn towards it their concavity 

 683b. 



