ORGANIZATION OF 'CRUSTACEANS. 71 



exposed, the animal might bleed to death, if it did not at once break off the 

 injured member at a particular point; namely, at a point in the second piece 

 from the body ; and by this operation, which seems to produce no pain, the 

 bleeding is effectually staunched. After this extraordinary amputation has 

 been effected, another leg begins to sprout from the stump, which soon 

 grows to be an efficient substitute for the lost extremity, and gradually, 

 though slowly, acquires the pristine form and dimensions of its predecessor. 

 The process of reproduction is as follows: the broken extremity of the 

 second joint skins over, arid presents a smooth vascular membrane, at first 

 flat, but soon becoming conical as the limb begins to grow. As the growth 

 advances, the shape of the now member becomes apparent, and constrictions 

 appear, indicating the position of the articulation ; but the whole remains 

 unprotected by any hard covering, until the next change of the shell, after 

 which it appears in a proper case, being, however, still considerably smaller 

 than the corresponding claw on the opoosite side of the body, although 

 equally perfect in all its parts. 



5. The nervous system of crusta'ceans is considerably develop- 

 ed : the ganglia of the head and thorax are large, and the latter 

 are sometimes united in a single mass. Most of these animals 

 have eyes of a very complicated structure. In general each one 

 of these organs is composed of an assemblage of a multitude of 

 little eyes, and the cornea covering each presents a considerable 

 number of square or hexagonal facets corresponding with it. 

 Sometimes these compound eyes are very slightly projecting, 

 sometimes, on the contrary, they are placed at^ the end of two 

 movable stems which are fixed on the front part of the head ; by 

 means of these peduncles or stems they can be directed forwards 

 or thrown backwards, in a kind of orbit (as in crabs, Jig. 63). 

 In most crusta'ceans too, we observe an organ of hearing, which 

 consists of a small tubercle, situated between the mouth and the 

 base of the external antennae, enclosing a small vesicle filled with 

 water, and the termination of the acoustic nerve. From the 

 stony nature of the skin, their sense of touch must be very 

 obtuse. 



6. The legs of crusta'ceans do not serve them for walking or 

 swimming only; in general, the first pair terminate in a sort of 

 pincers (called chela], by aid of which the animal seizes its prey 

 (fig. 61). 



7. Most of these animals are carnivorous ; some are parasites, 

 and live on other animals, whose blood they suck by means of a 

 kind of trunk ; but most of them feed on solid food, and have 

 mouths armed with strong jaws, often numbering six pairs. The 

 stomach is situated immediately under the mouth in the .interior 

 part of the body (Jig. 62, e) ; it is large, and its parietes are 



5. What, is the character of the eyes in crusta'ceans ? Have they an 

 organ of hearing ? 



6. What is meant by chela ? 



7. Upon what do crusta'ceans feed ? 



