PHYSIOLOGY OF INSECTS. 117 



by means of a distinct and free joint instead of 

 a sutural fixed line : it has this form in the tiger- 

 beetles. 



418. The helmet (galea) is situated on the 

 back of the feeler-jaw, behind the blade, and 

 before the feeler ; its variations are very nu- 

 merous, and, consequently, very useful in assign- 

 ing characters to insects. 



419. A palpiform helmet (galea palpiformis) 

 is when it is perfectly distinct from the blade, 

 and composed of one, two, three, or four cylin- 

 drical joints, like those of the feelers or 

 antennae : it has this form in carnivorous 

 beetles. 



420. An obtuse helmet (^aZea oftteso) is when 

 it appears simply as a shapeless mass ; it assumes 

 this form frequently when the lacinia is also 

 obtuse, and much resembles it in appearance. 



421. An obsolete helmet (<;a?€a obsoleta) is 

 when it is closely united to the blade : sometimes 

 a mere sutural line, and occasionally not even 

 that, denotes any separation between them. 



422. The maxillary feeler (maxipalpus) rises 

 from the feeler-bearer immediately behind the 

 helmet ; its principal variations are in the num- 

 .ber, form, and proportion of its joints : the 

 description of these are very simple, and easily 

 understood, without the employment of any set 

 terms. 



423. The mandibles (mandibulce) are situated 



