12 INJURIOUS AND USEFUL INSECTS 



in Orthoptera (to which the cockroach belongs), corre- 

 sponding to the pupa or chrysalis of most other orders, 

 but the insect runs about and seeks its food throughout life. 

 Between the last moult and the last but one, slight external 

 indications appear of the growing wings and wing-covers. The 

 angles of the mid and hind thoracic terga project backwards, 

 especially in the male, and on dissection the crumpled-up 

 wings and wing-covers are seen within the outer cuticle. 



3. (PEACTICAL.) THE MOUTH-PARTS OF AN 

 ORTHOPTEUOUS INSECT {Cocktoacb) 



The parts of the head previously removed (see p. 7) may 

 be prepared for mounting, or else the same parts may be 

 removed from a fresh head. If it is necessary to remove 

 the soft parts without loss of time, proceed as recommended 

 in the following paragraph ; but if the parts have been already 

 cleared by potash, soak in clean water, and go on from that 

 point. 



Place the bisected head, the labium, and the two maxillfe (see 



p. 7) in a porcelain saucer 

 containing a solution of 

 caustic potash (say five per 

 cent.). Heat this over a 

 Bunsen flame, using a 

 saucer of sand to prevent 

 excessive heating in one 

 place. Allow the solution 

 to boil for ten minutes. A 

 large number of parts may 

 be boiled in one saucer, if 

 several students are work- 

 ing together. Take care not 

 to bring the face near the boiling liquid, which is corrosive, and 

 rather apt to spurt when strongly heated. When the boiling 

 has been continued for ten minutes withdraw the flame. 

 Lift out the parts, now reduced by the action of the alkaline 

 fluid to chitinous skeletons, and place them in a saucer of 

 clean water. All the muscles and other soft parts will have 

 disappeared, and the chitinous pieces will have become more 



Fi^. II. — Back (to left) nnd front 

 (to right) views of the mandible of the 

 cockroach. X 20. 



