28 PRACTICAL ZOOLOGY. 



ring of the abdomen. In the same way remove the 

 second and first maxillipeds of this side, keeping them 

 in order. Are there gills attached to the maxillipeds? 

 Is there more than one gill on each leg? Are there 

 other gills than those attached to the legs ? Pick one 

 of the gills to pieces under water to determine its 

 structure. After removing the gills, look in this 

 region for further traces of thoracic rings. 



10. Anterior to the maxillipeds are two pairs of maxillae. 

 These are very thin, and lie close to each other, so 

 that if great care be not taken, they are likely to be 

 pulled off together. Investigate closely, and then, 

 inserting the forceps well down, remove them, one at 

 a time. Attached to the base of the hinder maxilla 

 is a thin, double-spoon-shaped structure, the gill- 

 scoop. It lies in the front part of the cavity in 

 which the gills are, the gill -chamber. With the 

 forceps move back and forth the second maxilla of 

 the other side, to see how the gill-scoop is thereby 

 moved. The gill-scoop, swinging back and forth, 

 pushes the water out of the front end of the gill- 

 chamber. The water thus expelled is replaced by 

 fresh water, which comes up under the lower edge of 

 the carapace, about the bases of the legs; thus the 

 gills are constantly bathed with water containing 

 a fresh supply of oxygen. 



11. The mandibles are short, hard, toothed, each bearing 

 a jointed appendage, which curves around the anterior 

 edge of the mandible in a groove. This is the mandib- 

 ular palpus. Move the mandible about to see how 

 it is hinged. Closely fitting against the posterior 

 surface of each mandible is a thin leaf-like structure, 



