THE BREATHING APPARATUS 



297 



city of the membrane, and the expelled water is thus 

 prevented from returning. 

 On the other hand, a new 

 supply of water can now 

 enter through the openings 

 at the sides of the maxillas, 

 and these openings in their 

 turn are then closed by the 

 forward movement of the 

 gill-plates. By this means 

 the gills are kept washed 

 by a continually fresh cur- 

 rent of water, of essential 

 service to the health and 

 vital energy of the animal, 

 although it is obvious that 

 the creature when burying 

 itself in the sand can for a 

 time dispense with this mode 

 of aerating its blood. . Jn 

 the Epicaridea, a group of 

 Isopoda, to be mentioned 

 hereafter, the marsupial 

 plates of the first gnatho- 

 pods (second maxillipeds) 

 have a function similar to 

 that of the epipods just de- 

 scribed. 



In the egg bearing fe- 

 males of the Cumacea, the 

 second pair of maxillipeds 

 have at their base a broad 

 fan directed stnvght back- 

 wards within the ventral 

 body wall. This is formed 

 by the two epipods, each 

 represented by a small round 

 plate armed on its tree mar- FIG. 24. masMis stygia,s&rs. First 



ji -i , illiped, with Oranchial apparatus, female 



gin with several long setse. specimen 



