8o Descriptive Zoology. 



are regarded as the highest, and probably the latest, of the 

 crustaceans. While the development of the individual does 

 not recapitulate the development of the race quite so fully 

 as in some other groups, it serves very well to illustrate the 

 general law that the development of 

 the individuals of the highest group 

 is an epitome of the development of 

 the group as a whole, and often is a 

 recapitulation of the order of geo- 

 logical succession. 

 FIG. 52. OYSTER CRAB. 



Cephalization. By this term is meant the 



higher development of the head, and of the appendages belonging to and 

 immediately surrounding the head. In the lower forms of crustaceans 

 the head does not predominate as in the crabs. The diameter is ap- 

 proximately the same from one end to the other. Even in the crayfish, 

 the ganglion at the anterior end is very little larger or better developed 

 than those of the abdomen. In the crabs there is a much greater con- 

 centration of the ganglions in the thoracic region. This principle will 

 be illustrated in other groups of animals, but it can be seen here that the 

 higher in the scale, the greater is the development of the head regions. 



The Sand Crab. This crab, with numerous . others, lives out of 

 the water considerable of the time. It is sandy in color, and lives 

 out on the beach. It seems to be rather keen sighted, and runs at 

 a lively rate when pursued. It usually attempts to escape, and often 

 succeeds, by burying itself in the sand. This it does in a wonderfully 

 short time. With a few quick, jerky motions of its legs it buries itself, 

 usually leaving only the tips of its two eyes projecting above the surface. 

 It is practically concealed, so much so that one who has pursued it, 

 unless he looks closely, may lose sight of it ; but the crab has its enemy 

 in sight all the time. Its means of escape is ingenious, and the color is 

 a fine example of protective resemblance. 



The Fiddler Crab. This little crab, about two inches wide, has one 

 big and one small pincher, suggesting the fiddle and bow. These very 

 interesting little fellows are sometimes so thick on the shore, along the 

 water line, that they crowd each other for crawling room, and make a 

 very noticeable rustling noise as they elbow each other while retreating 

 from the inquisitive biped, of whose motives they are suspicious. 



