Tue Brotocy or EpHypRA SUBOPACA LOEW 579 
leading cephalad to the pharyngeal skeleton (Plate LVII, 35). Ventrad to 
these two pairs just mentioned are two other pairs; the pair situated 
near the central ganglion are the mesothoracic disks, which will be 
developed as the mesothorax and the middle pair of legs, while the other 
pair anterior to them are the prothoracic disks for the prothorax and the 
anterior legs (Plate LVII, 36). These latter two pairs are similar in shape 
to each other, each having an elongated stalk leading out forward and 
connected with the ventral hypodermis. There are four pairs of disks on 
the dorsal tracheal trunks (Plate LVII, 37). In each trunk close behind 
the prothoracic stigma is the stalkless, and more or less bean-shaped, pro- 
notal disk embracing the tracheal stem (Plate LIV, 6). In the fourth 
segment is a disk, the largest of all, known as the mesonotal and wing 
disk. This disk is somewhat pear-shaped, is connected with the tracheal 
trunk, and has its stalk leading forward. Mesad and ventrad to this are 
two smaller disks. The anterior one is the mesothoracic disk, and the pos- 
terior is the metanotal and the haltere (Plate LVII, 38). To the external 
side of the hypostomal sclerite is attached an oval disk (Plate LVII, 37), 
and another is attached to the internal side of the sclerite. The former is 
the proboscis disk, and the latter the pharyngeal, which can be best seen 
in sections. Hewitt maintains that the maxillary disks are small and 
flask-shaped, and are found at the base of the oval lobes, but the writer 
is inclined to think these are probably a pair of sense organs. 
The abdominal disks.— Closely ventrad to the rectum is a pair of pear- 
shaped disks which have been considered as the rudiments of the external 
genital appendages. Differing from what has been found by Kiinkel 
d’Herculais (1875) in Volucella, the other pair is absent (Plate LVII, 37). 
The peripodal membrane is thin and transparent. When pupation 
commences, the differentiation of these rudiments can be seen through 
this delicate envelope. Each of the stalked disks has a nerve branch 
and a fine trachea. The parts that are sheathed within the peripodal 
membrane can be readily recognized (Plate LVII, 39 and 40). 
Growth 
Molting 
While making observations on the development of the larva after 
hatching, molting has frequently been noticed. As soon as the young 
larva attains its size, about three millimeters in length, the skin splits 
