114 Anopheles Maculipennis 
This structure is a kind of supporting collar ( anneau de soutien ) and is 
composed of cells which have no definite outlines and are in some cases 
vacuolated. It is invested by a connective-tissue coat, and is main¬ 
tained in position by some delicate muscle fibres arising from the head- 
capsule. Furthermore, it is also attached by means of fine membranous 
strands both to the connective-tissue coat of the oesophagus and, a little 
further forwards, to the commissure uniting the two cerebral ganglia 
(Figs. 17, 18 and 21). Posteriorly, the organ bifurcates into a pair of 
cellular prolongations (Fig. 16); while anteriorly it extends a short 
distance forwards between the cerebral ganglia. A similar structure has 
been described by Weismann (1864, PI. VIII, Fig. 8) in the larvae of 
Muscids and also by Lowne (pp. 88 and 91). It is, furthermore, found 
in the larvae of the Syrphidae (Kunckel de Herculais, 1875, PI. XIII, 
Fig. 5), of the Tachinid Thrixion (Pantel, 1898, p. 170) and of Sayomyia 
(Dogiel, 1877, Fig. 1). In the latter it is placed behind the brain as in 
Anopheles, but in Thrixion it lies for the most part above the cerebral 
commissure and in a more forward position. Dogiel states that in front 
of the collar the aorta divides into two lamellae, one of which extends 
under the brain towards the eye, and the other is more dorsally situated. 
At the point where the two lamellae arise the aorta opens freely into 
the haemocoelic space of the head. In Anopheles the further course of 
the aorta was found to be very difficult to follow, but it seems to divide 
into two lamellae as in Sayomyia , one of which is closely applied to the 
under surface of the cerebral commissure, and the other appears to be 
in intimate association with the dorsal surface of the anterior prolonga¬ 
tion of the anneau de soutien. 
The dorsal lamella in Sayomyia and Anopheles appears to be the 
homologue of the gouttiere susoesophagienne described by Pantel in the 
heart of the larva of the Tachinid genus Thrixion. 
The Oenocytes. 
Oenocytes are present in the larva of Anopheles and belong to two 
varieties—the large and the small. The large oenocytes (Fig. 26) are 
segmentally arranged in clusters, and are present in each of the first 
seven abdominal segments, but were not observed either in the 
eighth or ninth segments, and they are likewise wanting in the thorax. 
In each of the segments where they occur, they consist of two pairs of 
very large cells ou either side, which are situated a short distance 
beneath the hypodermis and towards the posterior margin of the 
