260 ANIMAL BIOLOGY. [Part II. 



of labial appendages. It consists of a sub-mentum (s. m.) and 

 mentum (m.), beyond which the labium is bifid, there being an 

 inner part, the lacinia (/.), and an outer part, the galea or para- 

 glossa (p. gl.), on each side, while labial palps (1. p.) spring from 

 the mentum. External to the labium are the maxillce. Each 

 has a basal part, the cardo (ca.\ which articulates with a pedicel 

 arising from the occipital rim. Articulating with the cardo is 

 the stipes (st.) y beyond which the maxilla is composed of two 

 parts : the inner, with sharp point and spinose blade, is the 

 lacinia (lac.) ; the outer, softer and setose, is the galea (ga.). 

 Where the galea joins the stipes springs the five-jointed 

 maxillary palp (mx. p.) The student should find little difficulty 

 in detaching and mounting the organs as figured. To get rid of 

 the soft tissues it should be boiled in a dilute solution of potash. 



It is not improbable that the mandibles, maxillse, and labium, 1 

 are homologous with the mandibles, first maxillse, and second 

 maxillse of the crayfish. It is not certain whether the antennae 

 of the cockroach and crayfish are homologous. 



Within the head is a complex, somewhat cruciform, chitinous 

 framework, the tentorium, for the support of the gullet and 

 brain, and the attachment of muscles. Nerve cords pass 

 through a central aperture, 



In the neck there are eight small cervical plates or sclerites : 

 two dorsal, somewhat triangular and apposed in the mid-line ; 

 four (two on each side) lateral, and somewhat oblique ; two 

 ventral, transverse and median, lying one behind the other. 



In each somite of the thorax there is a distinct dorsal or 

 tergal plate. The anterior of these, the pronotum, is the largest. 

 The posterior plate (metanotum) is slightly smaller than the mid- 

 plate (mesonotum). In the adult male the meso- and metanotum 

 are thin and semi-transparent. In each somite of the thorax 

 there is also a ventral plate, the sternum. The most anterior (pro- 

 sternum) is coffin-shaped, with the long axis placed longitudinally. 

 The mid-plate (mesosternum) shows indications in the male of 



1 The labrum is, in some insects (e.g. bees and their allies), regarded by 

 certain recent observers as originally double, and as an extreme example of the 

 coalescence of a pair of appendages. This is, however, doubtful. 



