No. 429.] THE MOUTH PARTS OF INSECTS. 793 
larval antenna. In the larva the antenna are very small com- 
pared with their size in the imago, and the imaginal antenna is 
thus forced, in its development, to occupy a region in the larval 
head not included in the larval antenna. But the tip of the 
imaginal organ lies fairly within the larval organ, thus indi- 
cating by correspondence in position, what is plainly obvious 
from anatomical consideration, the homology between the larval 
and imaginal organs. Similarly the forming imaginal mouth 
parts are to be found in unmistakable correspondence or 
homologous relation with the larval parts: By tracing the 
development of the parts, marked in Fig. 22 as the forming 
— 
SINUS RTT > 
5 : "app. 


Fic. 22. — S 1 1 of old 1 (y f 1 
head parts within. Zc., larval head wall; z.d., iiL derm ; Za. , larval anten enna; t.a., 
imaginal antenna ; z.e., imaginal eye; Zmd., terval mandible; Z2 €. imaginal mandible; 
lmz., larval maxilla; z.1x., imaginal maxilla ; /./., larval labium; 2./7., imaginal labiu: 
imaginal mouth parts, through larvae of successively older ages 
to pupation and the achievement of the definitive imaginal con- 
dition of these parts, it is certain that the parts marked respec- 
tively imaginal mandible, imaginal maxillz, and imaginal labium, 
lying respectively in the larval mandibles, maxilla, and labium 
(with homologies firmly based on ontogenic basis), do develop 
into those definitive imaginal parts named mandibles, maxille, 
and labium in Fig. 20, illustrating a dissection of the mouth 
Parts in a female adult Simulium. F ig. 23, a horizontal, frontal 
section through the head of a Simulium larva, shows also the 
forming imaginal maxilla and mandibles within corresponding 
parts, 
