40 THE AMERICAN NATURALIST. (VoL. XXXVI. 
usually on the cephalic side of the cephalo-lateral angle of 
the clypeus (Fig. 2, af). (It should be borne in mind that the 
cephalic margin of the clypeus is that margin which joins the 
front ; that morphologically the labrum is caudad of the clypeus.) 
It has been shown by Carriére and Bürger (97) that the 
position of this invagination in the young embryo indicates 
that it is the spiracle of the mandibular 
segment. It is easy to see that the 
migration cephalad of the antecoxal 
piece of the mandible, already described, 
would push this invagination into the 
position which it occupies in the adult 
insect. 
Bearing on this point is the fact that 
| in Smynthurus, according to Lubbock 
(73), the spiracles “open on the inner 
d asi E dh cork” side of the bases of the mandibles.” It 
; remains to be determined whether in 
this case the anterior arms of the ten- 
torium are wanting or not. Folsom 
(00) found that, although the three 
pairs of arms are present in the collem- 
bolan Orchesella, the anterior arms are 
wanting in Anurida. In Orchesella 
where the anterior arms are present 
they are described by Folsom ('99a) as 
being joined to the paraglossz (super- 
a | linguæ). Butas the invaginations form- 
par EP nre ing the anterior arms arise cephalad of 
the mandibles (Carriére and Bürger, 
'97), they cannot pertain to the superlingual segment. 
Usually the invagination forming the anterior arms is ex- 
tended to a greater or less degree along the sutures that con- 
verge upon it. This is well shown in Gryllus, where it is 
furnished with three buttress-like extensions : one along the 
suture between the front and the clypeus ; another between 
. the front and the gena ; and a third between the gena and the 
trochantin of the mandible. 













