162 [July. 



Both in its larval and adult states A. hilineata destroys Chortophila, its larvae 

 parasitising the pnparia, and its adults preying on the maggots of the fly. Its 

 larvae are, strictly speaking, ectoparasites, for though they penetrate th 

 puparia, yet they never enter the living bodies of the pupae. They exhibit a 

 simple kind of hypermetaniorphosis, the difference between the larvae of the 

 first and subsequent stages being considerable. With these remarks one may 

 pass to an actual summary of the life-history. 



The ova are deposited in the soil, and the larvae hatch in 10-12 days. They 

 are active, and about 1.5 mm. long. Their habitat is at the depth where the 

 puparia are found, and when brouglit to the svirface they at once begin to 

 burrow. It is essential for their development that they should enter dipterous 

 puparia, thoiigh whether they are restricted to those of C. brassicae is u.ncertain. 

 Having found a suitable puparium, the young larva gnaws its way in through 

 the wall thereof, an operation taking, in some cases at least, a considerable time. 

 The entrance-hole is nearly always dorsal or dor so-lateral, and circular. It 

 becomes filled with a white opaque substance, probably clotted fluid from within 

 the puparium. In some cases both host and parasite are killed by Nematode 

 worms or by a fungus, infections which probably enter through the hole made 

 by the Aleochara, either with the latter or before the hole is properly sealed up ; 

 the importance to the parasite of the effective sealing of the hole may therefore 

 be great. In only few instances does more than one larva enter a single 

 puparium, and in the observed cases where two or three did so, either none, or 

 only one, survived. 



The young larva, after its entry, may be seen moving slowly over the 

 pupa, apparently confining itself to the anterior dorsal surface. It feeds, and 

 before the first moult becomes much swollen. The larva of the second stadium 

 differs widely from that of the first. The cuticle is much less strongly chiti- 

 nised, the antennae and mouth-parts are much changed in form, the legs have 

 lost their claws and become indistinctly segmented, the anal cerci have dis- 

 appeared : the larva now presents all the characteristics of a parasite. It takes 

 up a definite position, nearly always on the dorsal surface of the pupa, with its 

 head near the junction of the head and thorax of the host. In this position it 

 absorbs the greater part of its food. Having exhausted the front part of the 

 pupa, it bends its head round and feeds on the hind parts, after which it 

 straightens itself again. 



The exact method of feeding is hard to ascertain in the first stadium, but 

 in the second it has been closely watched. The cuticle of the pupa is pierced 

 by the mandibles, and the semi-fluid contents are sucked out: the labium 

 works like a tongue, apparently with a lapping action, the maxillae move out- 

 wards and inwards, probably helping to press the fluid substances out of the 

 pupa, and the pharynx rhythmically expands and contracts. The cuticle of 

 the pupa is not eaten. 



The larva undergoes a second moult, but there is no further hyper- 

 metamorpliosis, the third stadium closely resembling the second in form. Two 

 days after feeding has ceased the excreta are got rid of, this action having 





