AXAXOMY OF THE GOUT-FLY OF BARLEV, 



801 



dorsal lobe ; the antenna! rudiment is, I believe, innervated 

 from the anterior region of the dorsal lobe, but I have not 

 been able to establish this quite definitely. The ocular half of 

 tlie inioginal sac overlies the anterior half of the corresponding 

 dorsal lobe. 



The process of evngination of the cephalic discs is believed to 

 he as follows:— The right and left sacs fuse in the median 

 lino a))oyo the cephalo-pharyngea.l band so that tlieir cavities 

 cominunicate. Tliis fusion gracUially extends forwaixls to include 

 tlio pediuiclcs wiioso central cavities come to form merely the 

 lateral regions of the peripodal cavity of the conjoined sacs, 

 V/hen this fusion extends as far forwards as the point of origin 

 of tlie peduncles from the pliaryngeal part of the cephalo- 

 pharyngeal band, which as mentioned above appears to be a 



Text-figure 11. 



Diiigriiin to show relations of ceplinlo-plmryngcal bjiiid, dorsiil vessel, and related 

 structures. The right dorsal lol)o of t!ie brain, and the right cephalic 

 imaginal sac are represented as having been removed ; left cephalic imaginal 

 sac and its peduncle not shown. Part of the cephalo-pharyngeal band 

 between the points E and E' is represented as having been removed. (Recon- 

 structed from serial sections and dissections.) 



double layered structure in this region, the two layers of the 

 band become more definite and split apart, the space between 

 the two layers being continuous posteriorly with the cavity of the 

 united imaginal sacs, and it is through this space that the 

 imaguial discs eva,ginate. I have not seen this process but, as is 

 mentioned below, the commencement of such a fusion of the sacs 

 and their peduncles has been seen in connection with the pro- 

 thoracic lea: discs. 



Thoracic Imaginal Discs. 



Oa. each side of the body there are three leg discs— prothor- 

 acic, mesothoracic, and metathoracic. From the antero-ventral 

 region of the sub-resophageal ganglion there arise on each 



