14 



Labium. — Remove the head of a locust and pin it with 

 the caudal aspect uppermost to a piece of cork. 



Note the freely movable flap which is the caudal part of 

 the mouth-parts. This and the crescent-shaped piece to 

 which it is attached form the lower lip or labium. 



The labium consists of the following parts : — 



Submentum. — The submentum is the proximal part of the 

 labium. It is nearly crescent-shaped, with long tapering 

 points, and is joined to the membrane which connects the 

 head with the thorax. 



Mentum. — This is the central portion of the labium ; and 

 is the principal part of that organ. It is articulated to the 

 distal margin of the submentum. To the distal margin of 

 the mentum are joined two movable flaps ; and to each lat- 

 eral margin is joined a process consisting of three segments. 



Labial Palpi. — These are the three-jointed processes of 

 which one is joined to each lateral margin of the mentum. 



Palpiger. — The labial palpi are not joined directly to the 

 mentum. There is on each side of the mentum a sclerite 

 which bears the palpus of that side and which is called the 

 palpiger. The suture between the palpiger of each side and 

 the mentum isalmost obsolete. Its position is indicated by 

 a slight groove which causes the palpiger to appear some- 

 what like a segment of the palpus, 



Ligula. — This is the distal portion of the labium. It con- 

 sists of two large movable flaps. 



Hypopharynx. — If the specimen has become dry so as to 

 be brittle, it should be softened with a little water. 



With the specimen pinned as in last section, carefully lift 

 the ligula so as to expose the maxillae. Note the tongue-like 

 organ which arises from the labium and from between the 

 maxillse. This is the hypopharynx. 



Remove the labium and place it on a glass slip in a drop 

 of Canada balsam or glycerine and cover it with a cover 



