THE CRAWFISH. 117 



of the powerful forceps at its end. Why are the blades 

 of the forceps roughened on their inner edges ? 



Is there any part in the foremost leg that is not present 

 in the other four ? 



There yet remain three pairs of small thoracic appen- 

 dages. These are the maxillipeds (or foot jaws). They 

 cover the mouth, being directed forward. The mouth opens 

 directly upward : probe between the maxillipeds to find 

 it. These maxillipeds, by the rubbing together of their 

 opposed segments, assist in the comminution of the food. 



Remove the hindmost maxilliped, and compare it in 

 structure with the typical abdominal appendage already 

 studied. Observe that it has a pedicel of two small seg- 

 ments, bearing two branches ; that it has (and the swim- 

 meret has not) a gill on the inner side of the basal segment. 

 Remove the second maxilliped, and find in it all the parts 

 present in the third. 



Remove the first maxilliped, and find the same parts 

 found in the other two, except the gill. In the place of 

 the gill, there is a broad plate, on the inner side of its 

 basal segment. The vertical series of gills begins with the 

 second maxilliped. Observe that the second and first 

 maxillipeds are much smaller and softer than the third. 



The remaining appendages are believed to belong to 

 the head. 



Closely following the maxillipeds, and covered by them, 

 are two pairs of very thin and delicate maxillae. These 

 are small, and closely appressed, and in removing them 

 care must be taken to separate them, and to take them 

 with the forceps by their basal segment. 



Before removing the maxillye, the gill scoop attached to 

 the second one should be seen in place. It is a curved 

 plate, attached to the outer side of the maxilla ; it plays 

 backward and forward in the anterior opening of the gill 

 chamber, and by a sort of sculling action propels the water 



