NUMBER OF HEAD-SEGMENTS IN INSECTS. 285 
fourth (labial) segment is quite separate from the rest of the head. 
Fig. 11 (in text), copied from our Memoir, also 
shows in a saw tly larva (Nematus ventricosus) the 
relations of the labial or fourth segment to the 
rest of the head. The suture between the labial 
segment and the pre-oral part of the head disap- 
pears in adult life. From this sketch it would 
seem that the back part of the head, i. e., of the 
epicranium, may be made up in part of the tergite 
or pleurites of the mandibular segment, since the Fl0 u _ Heiul of eml)rV(> 
mandibular muscles are inserted on the roof of the Ncmatu . s ’ 8ho ' viu ? tll « labial 
segment, occ , forming the occi- 
head behind the eyes. It is this segment which pup ciypeua; labrum ■ 
” ° md, mandible; mdm, muscle or 
in Oorydalis evidently forms the occiput, and of same; mx, maxiiia; m%\ 
" 7 ... maxilla (labium) ; oes, ooaopha- 
which in most other insects there is no trace in gus. 
larval or adult life. 
It appears, then, that the epicranium, or that piece (sclerite) bearing 
the eyes, ocelli, and antennae, and in front the clypeus and labrum, is 
formed from the original procephalic lobes, and represents the first or 
antennal segment, and is pleural, the clypeus and labrum being the ter- 
gal portion of the segment; while the remainder of the original or primi- 
tive segments are obsolete, except in those insects which retain traces 
of an occiput or fourth cephalic tergite. All of the gular region of the 
head probably represents the base of the primitive second maxillae. 
