JOINTED-LIMBED ANIMALS WHICH BREATHE IN WATER 401 



inclusive. If these joint-gills are folded back in their turn, four 

 side-gills become apparent, so called because they grow out from 

 the side wall of the body. They correspond to the last four seg- 

 ments of the thorax, which bear the four pairs of walking-legs. 

 Each limb-gill is associated with a plate-like outgrowth (epipod) 



Anlcnnu/c 



FJ^. 532. Gills of Right Side of Lobster (Homarus vulgaris), reduced. 



The gill-cover has been removed, the pincers (i) and four walking-legs (n-v) cut short: 1-7, segments of abdomen 

 and their appendages; aaaa, limb-gills (two last turned down); bb, joint-gills 



from the limb to which it belongs, and the chief use of these 

 plates appears to be to help to keep the gills separate, so that 

 water may pass between them. From what has been said it 

 will be seen that there are twenty gills in all on each side of 

 the body, and this is most easily understood by presenting the 

 facts, for one side, in a tabular form. 



GILL-FORMULA OF LOBSTER (SIMPLIFIED AFTER HUXLEY). 



VOL. II. 



6 



10 



+ 4-20 



58 



