274 



THE SEA SHOES 



same time we may discover the bailing organ by means of which a 

 current of water is kept flowing forwards through the gill-cavity 

 to keep up the necessary supply of oxygen for respiration. The 

 removal of the upper portion of the carapace will expose the heart 

 and some of the principal bloodvessels, and also the stomach with 

 its powerful and complicated ' gastric mill,' formed by the harden- 

 ing of portions of the wall of the latter organ for the purpose of 

 crushing and masticating the food. Then, if these organs be care- 

 fully removed from above, together with the others we have not 

 space to describe, and the powerful muscles that fill up the segments 

 of the abdomen, the chain of ganglia and their connecting nerve 



FIG. 206. LONGITUDINAL SECTION OF THE LOBSTER 



a, antenna; r, rostrum or beak; o, eye; m, mouth ; s, stomach ; in, intestine; 

 I, liver ; gl, gills ; h, heart ; g, genital organ ; ar, artery ; n, nerve ganglia 



cords that form the central part of the nervous system may be seen 

 extending along the central portion of the body. 



Several species of lobsters inhabit our seas, but they are gene- 

 rally to be found beyond the tide-marks, and are, therefore, not 

 often caught by sea-side collectors without the aid of some kind of 

 trap or the assistance of fishermen. The common lobster (Homarus 

 vulyaris), however, is often left behind by the receding tide on our 

 rocky coasts, and may be seen and caught if one knows where to 

 look and how to capture. 



On cautiously approaching a deep rock pool one may often see 

 a lobster rapidly retreat in its usual backward fashion, and snugly 

 house itself in a narrow chink from which it is impossible to remove 

 it. And, when once surprised, it is not likely to show itself again 

 as long as the intruder is in view. 



