578 Cutu PING 
one dorsal; the dorsal wing is attached to the dorsal body wall, while the 
two lateral wings are attached to the lateral body wall. These wings 
are, however, smaller. The pericardium is profusely supplied with 
tracheae (Plate LVI, 33), as has been found in other dipterous larvae, 
such as Musea, Calliphora, Psychoda, and Anopheles. 
The reproductive system.—In the mature larva a pair of gonads is found 
in the fifth abdominal segment. They are imbedded in the fat bodies and 
ach has its duet leading posteriorly to the ventral body wall. They 
are pyriform, and at the posterior end there is an accumulation of imaginal 
disks. The general arrangement of cells in the gonads (Plate LVI, 34) 
is similar to that described by Weismann (1864) in the larva of Musca 
vomitoria, and according to his description these gonads are a pair of 
testes. 
The imaginal disks — The imaginal disks in the larva are of two kinds, 
the paired and the unpaired. The latter are insignificant and developed 
later, while the former are prominent and perfect in shape as soon as the 
larva enters the third instar. The unpaired disks are found in the 
alimentary canal and in the hypodermis, and they have to do with the 
development of the future fly. The writer has not been able to find 
the hypodermal rudiments in his preparations, because they are developed 
after pupation commences. Those scattered in the alimentary canal are 
similar in shape to those found in the larva of Musca. They are located 
at the anterior end of the proventriculus, all over the mid-intestine, behind 
the base of the malpighian tubes, surrounding the anus, and at the anterior 
end of the salivary glands, as figured by Kowalevsky (Plate LY, 14). 
The paired disks may be again divided into two groups according to their 
locations, namely, the ecephalothoracie and the abdominal disks. 
The cephalothoracie disks — There are eleven pairs of disks in this 
region. They are the centers of development for the different parts of 
the imaginal head and thorax, and their appendages. Closely adjacent 
to the cerebral lobes is the pair of optic disks, which are connected with 
the lobes through the optie stalks. The optie disks are applied to the 
front of the lobes with their posterior coneave surface, while their anterior 
convex surface is connected with a stalk leading to the antennal and 
frontal disks. The two pairs can be distinguished in sections. The 
antennal disks, more or less elliptical in outline, lying between the optic 
disks and the cephalopharyngeal skeleton, terminate in elongated stalks, 
