118 INVERTEBRATE ZOOLOGY. 



and "shank" (tibia), the angle between them being termed the 

 "knee." Between the body and the thigh are interposed two little 

 joints, coxa and trochanter. Below the tibia extends the foot or 

 tarsus. This typically consists of five joints, the terminal one bear- 

 ing a pair of claws (ungues), but in the grasshopper the number is 

 reduced to three. Examine the %mlvilli, or little pads, at the bottom 

 of the feet and see if you can explain this. Draw one of the legs. 



6. Abdomen. The somites here conform nearly to the tj^pe, but lack 

 appendages and pleurites. They consist of tergite and sternite, and 

 are regular and plain except the first, which is fused ventrally with 

 the thorax, and at the end, where they are modified to accommodate 

 the reproductive organs and the outlet of the intestine. In this they 

 differ in the two sexes. In the female are four long hooks, the rhab- 

 dites or egg-giiides. The ducts of the germ glands, and the alimen- 

 tary canal have their outlets among these terminal plates. Keep this 

 in mind and find the relationship of these parts, during the dissection 

 of these systems. In the dorsal portion of the first segment, under- 

 neath the wing, will be seen the ear, a vibratory membrane stretched 

 across a cavity. 



93. Digestive system. For all internal dissections, use fresh specimens 

 and as large as possible. Hold the animal in the left hand with the head 

 toward you, and clip off with the scissors the legs, wings and antennae. 

 Then insert the point of the scissors just beneath the anterior edge of the pro- 

 notum, at the place where it bends over laterally, and cut through the exo- 

 skeleton, keeping on the side, as far as the end of the abdomen. Make a sim- 

 ilar incision on the other side. In this, keep the concealed point of the instru- 

 ment as near as possible the inner surface of the exo-skeleton, in order not to 

 woiTud the parts beneath. Then pin the animal to the wax of a small glass 

 dissecting pan, running the pins through the incision, close to the lateral 

 walls. Cover the specimen with 30 j? and place the pan upon a dissecting 

 microscope. Take the forceps in the left hand and the scalpel in the right, 

 and lift off the free dorsal piece, cutting off the connections as close as pos- 

 sible to the part to be removed. The internal organs will be seen lying in 

 place in the ventral portion of the exo-skeleton, which thus serves as a shell. 

 The alcohol renders transparent parts opaque, and the use of a liquid in dis- 

 section is for the purpose of imfolding delicate membranes, etc., which would 

 remain in air as a confused heap. (cf. the use of water in mounting " sea 

 mosses.") If the pins be gentl.y spread out, the walls ^vill widen a little. The 



