938 C. GORDON HEWITT. 
by means of an anterior and a posterior pair of spiracles. 
The anterior spiracles, which do not occur in the first larval 
instar, are considered to be functional. 
12. The vascular system consists of: (1) A dorsal vessel, 
the posterior region of which is swollen to form a cardiac 
region or “heart”? which communicates with a pericardial 
cavity by means of three pairs of lateral ostia; (2) the great 
ventral sinus, which forms the body cavity; and (3) the peri- 
cardial sinus. The pericardium is well supplied with trachez, 
which may assist in respiration, as in certain other insect 
larvee. The adipose tissue cells which compose the large 
lamin forming the fat-body are similar in structure to those 
of the fly. 
13. Three groups of imaginal rudiments or discs can be 
recognised in the larva: (1) The cephalic discs, of which two 
appendicular pairs are situated at the anterior end of the larva 
and three pairs in front of the cerebral lobes of the ganglion ; 
(2) the thoracic dises, two pairs of which are attached to the 
anterior end of the ventral side of the ganglion, and three 
pairs are connected with the lateral tracheal trunks in the fifth 
segment; (3) the abdominal and visceral discs. 
VII. Literature, 
For the sake of convenience a few of the references given 
in Part I have been repeated here. 
1962. BrriEesn, A.— L’accoppiamento della Mosca domestica,” ‘ Rev. 
Patalog. vegetale,’ vol. ix, pp. 8345—357, 12 figs. 
1834. Boucug, P. Fr.—‘ Naturgeschichte der Insekten besonders in hinsicht 
ihrer ersten Zustande als Larven und Puppen,’ Berlin, 216 pp., 
10 pls. (M. domestica, pp. 65, 66, pl. v, figs. 20—24.) 
1883. Bravrr, F.—“<Die Zweifluger des kaiserlichen Museums zu Wien: 
ILI. Systematische Studien auf Grundlage der Dipteren larven nebst 
einer Zusammenstellung von Beispielen aus Literatur tiber dieselben 
und Beschreibung neur Formen,” ‘Denkschr. der Kais. Akad. der 
Wiss. math-naturwiss. Classe,’ Wien, vol. xlvii, pp. 1—100, 5 pls. 
