24 INVERTEBRATE ZOOLOGY 



boundary between the head and the thorax. In the crayfish 

 two semicircular, longitudinal grooves extend backward from 

 the outer ends of the cervical suture, which separate the sides 

 of the carapace from the median, dorsal portion. The sides of 

 the carapace are called the branchiostegites ; they cover lateral 

 folds of the dorsal integument of the animal, which extend 

 over the sides of the body and enclose between themselves and 

 it the spaces within which lie the gills. These spaces, the gill- 

 chambers, thus communicate freely with the surrounding water. 

 Pass the handle of a scalpel or other flat object beneath the 

 lower edge of the branchiostegite and it will go into the gill- 

 chamber. During life a current of water passes constantly 

 into the gill-chamber along this lower edge, where it bathes the 

 gills and then passes out at the forward end. 



Study the ventral side of the cephalo thorax. The most 

 important organs here are the appendages. At the anterior 

 end of the body are the two pairs of antennae, the longer pair 

 being the second. On the lower surface of the basal joint of 

 each of the latter is an opening ; these are the external open- 

 ings of the kidneys or green glands. Back of the antennae is 

 the mouth. It is bounded in front by a lip-like structure called 

 the labrum, at the sides by the strong mandibles, and behind by 

 a pair of delicate plate-like projections, called the paragnatha, 

 which are not appendages. Press the mandibles aside and 

 pass a probe into the mouth. Between the mouth and the 

 large claws are five pairs of appendages which assist in the 

 act of eating ; they are two pairs of delicate leaf-like maxillae, 

 just back of the mouth, and three pairs of larger maxillipeds, 

 back of them. They are best identified by beginning with 

 the hinder pair of maxillipeds, which is just in front of the 

 large claws, and working forward, placing a needle or knife 

 between the appendages as they are identified. Back of the 

 maxillipeds come the large grasping claws or chelipeds, which form 

 the principal weapons of offense and defense of the animal, and 



