526 EXTERNAL ANATOMY OF INSECTS. 



In some aquatic genera of beetles, as Gyrinus, Parnus, 

 &c. they are withdrawn within a lateral cavity of the 

 same part, and are defended from the water externally 

 by the auricle at their base a . The flabellated and la- 

 mellated antennae, previous to their being folded for re- 

 pose, close all their plates; which in action are as widely 

 expanded as possible, so as to form a knob; and in some 

 the middle piece is entirely concealed, as if in a box. 

 In broken antennas, or those in which the clavolet forms 

 an angle with the scape, the former is folded upon the 

 latter, with its point downwards. 



II. Subfacies. — Having dispatched the Fades, or up- 

 per side of the head, I am next to consider the Sub- 

 facies, or under side : but as the principal parts that oc- 

 cupy this side have been already considered, I shall have 

 no occasion to detain you long. 



i. Jugidum b . — This part, which may be regarded as 

 analogous to the throat in vertebrate animals, lies between 

 the cheeks ; from which it may usually be distinguished 

 by being more lubricous and tumid, and often separated 

 by an impressed line. It is particularly conspicuous and 

 elevated in the Lamellicorn beetles, and calculated by its 

 lubricity for easy motion in the lower side of the cavity 

 of the chest. Its apex is the base in which the mentum 

 sits. It is not necessary to enlarge further upon it, as it 

 seldom exhibits striking characters. 



III. Collum c . — In a large proportion of insects the 

 head inosculates in the trunk without the intervention 



a Plate XII. Fig. 29. a. "> Plate VI. m. « Ibid. 



