800 MK. J. 0. II. FllEW ON TJIE l.AllVAL 



of any segment arise close together from the mid-lateral region 

 of that segment, slightly ventro-lateral to the dorso- lateral 

 tracheal trunk. Each arises by a sliort dorsal and a short 

 ventral root, Avhich unite to form a very thin strap-like muscle 

 Avhich passes inwards and dorsally below the dorso-lateral 

 tracheal trunk to the pericardial cell to which it is related. Here 

 in splits into dorsal and ventral layeis Avhich are inserted 

 res})ectively into the dorsal find ventral walls of the dorsal vessel, 

 iind between which lies the pericardial cell. The dorsal and 

 ventral layers do not retain their narrow strap-like form but 

 spread out fanwise in the antero-posterior direction, so that the 

 anterior ends of their insertions into the heart extend as fii.r 

 forwards as the posterior endsoF the insertions of the alar muscles 

 next in front of them. The ligures given by Imms (8, ligs. 9 

 <t 10, PI. ix.) show the arrangement of the ah\.r muscles in rela- 

 tion to the dorsal vessel in Ano]jheles, and the arrangement in 

 Chloraps is almost identical. 



Ventral Neplirocytes. 



In Muscid hirvte the ventral nephrocytes usually foi-m a, trams- 

 verse loop of cells passing below the gut, each end of the loop 

 being attached to one of the salivary glands at the junction of 

 the glandular region and duct. In Chlorops, however, the ventral 

 nephrocytes consist of two separate masses each of seven or eight 

 cells, the groups lying one at the anterior end of each salivary 

 "land between the gland and the proventriculus and attached to 

 the gland at the region of junction of the duct with the glandular 

 portion. These cells are very much smaller than the dorsal ' 

 nephrocytes and are binucleate ; they also differ from the dorsal 

 nephrocytes in several cytological details which will not, how- 

 ever, be considered here. 



QJnooi/tes occur in each of abdominal segments 1 to 7 inclusive, 

 as two groups of about five or six cells, the groups lying one on each 

 side of the segment close against the hypoderm in the mid-lateial 

 i-e^ion. The cells are all uninucleate with rather dense, finely 

 granular, and nonvacuolated protoplasm. 



^Sinall Gcnocytes (8) appear to be absent. 



The Fat Body consists of lobes and chains of large cells lying 

 between the various organs of the body. There is no fat body 

 in the head and very little in the thoracic segments. 



Integument, 



The chitin consists of two layers, an outer thin and dark 

 coloured, and an inner thick and light coloured. The surfaces 

 of the two layers where they come in contact are very minutely 

 serrated, the serrations engaging with each other. Tlie hori- 

 zontal split by which the puparium will open is marked out in 

 the third instar larva by what is apparently a closed fissure, 

 appearing in sections as a thin dark line through the chitin, 

 which passes horizontally round the anterior end of the larva 



