ZOOLOGICAL SOCIETY BULLETIN 



1177 



CRABBERS AT WORK 



AIniiK- an inlet on the south shore of Lon;; Nliuid. with 

 tiox and folding traps. 



gettino- tliem tangled uj). Morever, his body is 

 pointed at the sides and thus there is much less 

 resistance in this direction. Someone has sug- 

 gested tliat the motto of the crab should be "be 

 sure you're right and go sideways tor all you're 

 worth " and certain persons, probably not zoo- 

 logists, have spoken slightingly with regard to 

 this lateral progression of the crab, as though 

 he were not advancing as the result of his 

 labors. Of this one thing we may be sure, the 

 crab goes where he wants to go and wastes no 

 time about it, which is perhaps more than can 

 be truthfully said of some of his critics. 



Like other higiier crustaceans, the crab 

 breathes by gills, which while morphologically 

 outside of the body, have become enclosed by 

 the projection of the shell so that they are com- 

 pletely covered and jirotected. The only open- 

 ings left are those at the bases of the legs. 

 where the water enters the gill chamber and at 

 the anterior end of this chamber where the 

 water, depleted of its oxygen and laden with 

 carbonic acid gas, finds its exit. The gills are 

 outgrowths from the bases of the legs, in the 



form of complicated feathery structures, in 

 which the colorless blood is exposed over a 

 large area to the water in the gill chamber, with 

 only a thin layer of tissue between. One of the 

 interesting things about the manner of breath- 

 ing is the fact that fresh water is not sucked 

 or otherwise forced into the gill chambers, but 

 instead is dijiped out by the .action of a peculi.ir 

 spoonlike organ on the base of tiie tiiird jaw- 

 foot or maxilliped. These structures, of course, 

 are arranged bilaterally, that is, one on each 

 side of the body. This ladle, known techni- 

 cally as the scapiiognathite, is kept in constant 

 motion, dipjjing out the water so that a new 

 sujjply containing oxygen may enter the gill 

 chamber through the small openings in the shell 

 at the bases of the legs. The openings of the 

 ducts of the excretory glands are situated far 

 fin-w.ird on the bases of the large second anten- 

 nae, and the current of the water from the gills 

 c.irries away the jiroducts of these glands. 



.\s h.is been stated, the pincers are not used 

 in locomotion, but serve for capturing and rend 

 ing the food and for self defense. The food 

 I roken off by the pincers is passed by them 

 directly to the mouth ))arts and it is an inter- 

 esting sight to watch these ungainly appendages 

 during this operation. The mouth ji.irts number 

 six |),iirs, all of them jointed and working from 

 side to side. The study of their origin |)roves 

 tiiat all of these were originally legs, three 

 pairs of them belonging to the head region and 

 three to the thorax. The most anterior is a 

 ])air of crushing organs, called mandibles, .and 

 behind these are two jiairs of cutting imple- 

 ments, the maxillae. The three thoracic pairs 

 of mouth )3arts, the maxillipeds (jaw feet) aid 

 in holding and breaking up the food, while to 

 the hinder one is attached a ladle for dipping 

 out the water from the gill chamber. Another 

 portion of this same jjair takes the form of .1 

 broad expansion which can be closed over the 

 other mouth parts like a ])air of trajj doors. 



The body of the crab is so condensed, and 

 abbreviated at the ends that at first glance it 

 appears like a thorax running about minus the 

 head and abdomen. A little closer scrutiny will 

 show that the head is simply fused with the 

 thorax after the fashion of the lobster only 

 very much more so. Its position is indicated by 

 the two pairs of antennae or feelers and the 

 bright shining compound eyes, mounted on 

 movable stalks. The later can be tucked away 

 beneath the shell for protection, or protruded 

 for purposes, of observation. 



The abdomen, which at first appears to be 

 entirely lacking in the crab is found to be bent 

 forward under the thorax, though to be sure, 



