200 
J. Rennie and C. II. Sutherland 
cases the prothoracic spiracles show a different number of lobes in the same 
larva, e.g. one spiracle has seven, the other eight lobes (figs. 20-24). 
The post-abdominal spiracles are borne on two tubercles arising from the 
terminal segment. These tubercles are surrounded by a chitinous hoop which 
is open and flattened on the inner side. Each tubercle is again bilobed, each 
secondary lobe opening to the exterior by two slits. Thus within the chitinous 
hoop there lie four slits. These slits are surrounded by oval peritremes whose 
internal border is dentate. The peritremes lie so that their axes converge 
towards the inner border of the collar. The spiracle tubercle shows two white 
spots, the openings of perispiracular glands (fig. 17). 
The spiracles communicate with the tracheal trunks through a ‘ felt- 
chamber which is a short tube filled with a spongy chitinous structure. 
On the ventral surface of the last abdominal segment lies the anus in the 
form of a cleft with a protuberance on each side. The posterior end of the larva 
moves freely in the chitinous funnel, and, as far as has been observed, the 
post-abdominal spiracles are never closely adpressed to the host trachea but 
the air from the host trachea is drawn into the chamber formed by the adhering 
chitinous funnel where it is at the disposal of the larva. 
Bucco-Pharyngeal Apparatus. 
The complete masticating apparatus of the mature larva of Bucentes 
geniculata consists of a number of paired sclerites, the members of each side 
articulating with one another to form a united whole (figs. 12 and 13). 
Overhanging the oral aperture is a pair of strong curved hooks, the 
mandibular sclerites. Dorso-posteriorly these have a dentate process, while 
ventro-laterally they bear a blunt wedge-shaped process. A ventral view 
shows the mandibular sclerites to be united by a cross bar. Each ventro¬ 
lateral process is perforated by a minute pore. 
Articulating with the posterior border of the mandibular sclerites are the 
hypostomal sclerites which are united ventrally by a transverse bar. Between 
the mandibular and hypostomal sclerites there lies ventrally a fused dentate 
sclerite which is perforate. 
The posterior extremities of the hypostomal sclerites articulate one on each 
side with the cephalo-pharyngeal sclerites, which have each a slight anterior 
rectangular prolongation, joining it to the hypostomal sclerite of its side. 
The cephalo-pharyngeal sclerites are prolonged dorsally, into wing-like pro¬ 
cesses which are perforate near their outer edges, and ventrally, into a stout 
somewhat rectangular posterior process which has a curved incision at its 
extremity. 
The cephalo-pharyngeal sclerites articulate ventrally with a broad chitinous 
plate, the floor of the pharynx, as do also the extremities of the posterior 
ventral processes. 
The Puparium (fig. 14). The puparium is brown in colour, barrel-shaped 
and with clearly marked segments. Each segment bears a double series of 
14—2 
