78 THOMPSON YATES LABORATORIES REPORT 
present on that portion of the maxilla from which the papillae arise. In a transverse 
section of the maxillae near their tips they present a peculiar jaw-like shape 
(plate XV, fig. i). The maxillae appear to arise from the under surface of the maxillary 
palpi between them and the upper outer surface of the labium ; in transverse sections 
they appear in this region as two lateral sickle-shaped stout masses of chitin, situated on 
each side of the commencement of the hypopharynx (plate XVI, fig. 2). Each maxillae 
is continuous with a thick rod of chitin, which extends almost the whole length of the 
head, ending in a long upper and a lower shorter stumpy rounded process in the basal 
part of the occipital region. To these intercranial chitinous rods, which appear to lie 
free in the cellular tissue at the base of the head, powerful muscles connected with 
the movements ot the proboscis are attached (plate XIX, fig. 1 ; XVII, fig. 1 ; and 
XVIII, fig. 1). These processes have been variously termed ; byLowNE, 1 'apodemes;' 
by Macloskie, 2 the 'great tendons' of the mandibles. Gerstfeldt 5 regarded them 
as the basal portions or 'cardines ' of the hypopharynx. No mention is made of them 
by Packard 4 in his description of the insects' mouth parts. Smith 5 regards these 
basal processes found in various genera of diptera Bombylius, Anthrax, Eristalis, Musca, 
etc., as basal prolongations of the palpifers (the mandibles of other authors), and states 
they may perhaps represent the ' stipides ' as well — which he has not as yet identified 
in the dipterous mouth parts. It would seem from Dimmock's 6 account of the 
anatomy of Culex that these chitinous rods do not extend so far back into the head in 
this genus ; he says ' their continuations (of the maxilla) in the head are two delicate 
chitinous supports, each ot which ends in a strong muscle ; this muscle — the retractor 
maxillae — passes backwards and downwards through the head beneath the infra- 
oesophageal ganglion, and has its origin in the posterior basal part of the head.' That 
they are the supports from which the maxillae arise can be well seen in serial sections. 
The muscles in connection with the chitinous intra-cranial processes of the 
maxillae are : — 
1. Muscles fixing them to the cranial exoskeleton. Each has a large 
muscle which arises from the lower occipital region of the cranium 
and is attached to the outer side of the process for the greater 
part of its extent : the fibres of this muscle run horizontally ; 
muscle fibres, directed upwards, also run in connection with the 
terminal bifid extremity and that portion of the exoskeleton of 
the head, which is folded beneath the eyes (plate XIX, fig. 1 z.m.). 
2. A spindle-shaped belly of muscle arises from the ventral surfaces of 
the processes to be inserted into the base of the labium (plate 
XVII, fig. 1 ; XIX, fig. 1 l.m'). 
1. Lowne, The Anatomy and Physiology of the Bloiv-fly. London, 1870. 
2. Macloskie, The Proboscis of the House-fly. American Naturalist, 1880, vol. xiv, p. 153. 
3. Gerstfeldt, Ueber die Mundtheile der saugenden Insecten. Dorpat, 1853. 
4. Packard, Text-book of Entomology. New York, 1898. 
5. Smith, Trans. American Entom. Soc, vol. 17, 1890, p. 338. 
6. Dimmock, The Anatomy of the Mouth parts, etc. Boston, 1881. P. 16. 
