222 MYIASIS 



of the black paired nioulh-hooks may be seen protruding, while in a slight depression 

 in the flattened posterior surface of the twelfth segment are situated the paired 

 posterior stigmatic plates. In the adult larva the slit-like apertures in these plates 

 are not very easy to distinguish, but in a maggot in the second, or penultimate stage, 

 it is seen that each plate bears three ridges of tawny coloured chitin ; these ridges run 

 obliquely downwards and outwards, at an angle of 45° from the median vertical line, 

 and, while the median ridge on each plate is nearly straight, the other two ridges are 

 characteristically curved, resembling inverted notes of interrogation, with the 

 concavity directed towards the median ridge. The segments of the body are 

 transversely wrinkled on the dorsal and ventral surfaces (especially on the latter), and 

 puckered on the sides. From the third to the eleventh segment the body is thickly 

 covered with minute recurved spines of brownish chitin (darker in the case of larvae 

 ready to leave the host), usually arranged in transverse series or groups of two or 

 more, which can be seen to form more or less distinct, undulating or irregular, 

 transverse rows. These spines will be described in somewhat greater detail below. 



"Above and to the outer side of each mouth-hook is an antenna-like protuberance, 

 which, as in the case of the larva of the blow-fly {Calliphora e)-ytlirocephala iMg.), 

 exhibits a pair of light brown, ocellus-like spots, or rather papilla?, placed one above 

 the other. In a small larva, 5 mm. in length, from Lagos, the papillae are very 

 clearly visible ; each papilla is surrounded by a ring of pale brownish chitin, and its 

 shape, when viewed from the side, is exactly that of the muzzle of an old-fashioned 

 muzzle-loading cannon. 



"This small larva also shows on the basal segment of each antenna, or antenna-like 

 protuberance, below and a little to the outer side of the mouth-hook, a prominence 

 bearing a series of about six small, brown-tipped, chitinous spines. In the same larva 

 the spines on the body are most conspicuous, and most strongly developed and 

 chitinized, on the fifth, sixth and seventh segments. The tenth and eleventh segments 

 are also covered with spines, but, since the chitin of which they are composed is not 

 tinged with brown, these segments appear bare. In the adult larva also, the spines on 

 the tenth and eleventh are less conspicuous than those on the preceding segments ; 

 on the twelfth segment, which bears the posterior stigmatic plates, the spines are 

 very minute. Fully chitinized spines are dark brown, but this colour is generally 

 confined to the apical half of the spine, or may be absent from the extreme base. In 

 shape each spine is a short cone, with the apex recurved, pointing towards the 

 hinder part of the body. The spines are broad at the base in proportion to their 

 length, and not infrequently, especially on the under side of the body, are bifid at the 

 tip. They are closest together and most strongly developed on the anterior portion 

 of each segment, becoming smaller and showing a tendency to disappear towards the 

 hind margin. They are arranged in irregular transverse rows, which are usually seen 

 to be composed of groups of from two to five spines, placed side by side. 



"In the adult larva the median area of the ventral surface of the segments five 

 (or six) to eleven inclusive is marked with a series of three transverse ridges, which 

 are most prominently developed on the seventh and following segments. On each 

 segment the foremost ridge is the shortest ; next in length comes the hindmost, and 

 the middle ridge is the longest of the three, ending round the posterior ridge at each 

 end. Similar but less strongly marked ridges are seen on the dorsal surface. 



'' Pupariiiin. Of the usual liarrel-shaped Muscid type. Average dimensions: 

 length loi mm., greatest breadth 4I mm. Though at first of a ferruginous or light 

 chestnut tint, the puparium gradually darkens until it becomes ' seal brown ' or 

 practically black." 



