66 Laboratory Guide in Zoology- 



second and third divisions are not so well defined, 

 and do not move upon each other. The division may 

 be made out, however, by observing certain lines which 

 represent the union of the two. On the ventral surface 

 this line will be found behind the second pair of legs ; 

 trace it up along the sides and back. The middle seg- 

 ment thus distinguished is the mesothorax, and the hind 

 segment is the metathorax. 



IV. — Notice that the position of the head is at right 

 angles to- the body axis. Compare it in this respect 

 with the lobster. Study the long slender projections 

 — the antennae, or feelers — on the front of the head. 

 See with a lens their jointed structure. Notice the 

 pecuhar surface of the large compound eyes. Between 

 the compound eyes, find three small ocelli, or simple 

 eyes. 



V. — Begin the study of the mouth parts by finding on the 



lower side of the face a movable flap — the labium, or 

 upper lip. Observe this carefully, then remove it and 

 see directly beneath it the mandibles, or jaws, — one on 

 each side ; these are hard, black, toothed structures. 

 Press them apart, and then pull them out carefully with 

 pointed forceps. You thus bring into view a dark brown, 

 spindle-shaped organ in the centre of the mouth : this 

 is the ligula, or tongue. The entrance to the gullet is a 

 small round opening above the base of the tongue. 

 Below where the mandibles were, the maxillae are now 

 to be seen, one on each side. Pull one of these out, 

 being careful to get the whole of it, and by the aid of 

 a lens identify the following parts : — 



a. The basal segment. 



b. The jointed appendage on the outside, called the 

 maxillary palpus. 



