222 t-^^^y- 



eg^s of this parasitic fly, yet only a small percentage become parasitised. 

 Another Tachinid, Carcelia chelonae, lays its eggs on the caterpillar of the 

 Brown-tail Moth, but many of its eggs and new-hatched larvae are destroyed 

 by becoming impaled on the bristles and barbed hairs of the caterpillar. Again, 

 Datanid caterpillars have a hard head-capsnle and a hard dorsal sliield on the 

 last segment ; when disturbed they elevate their anterior and posterior 

 extremities, so that the body is curved in a semi-circle, and consequently the 

 two hard surfaces are the principal parts exposed to Tachinid flies hovering 

 above. Hence the hard shields, which are impenetrable to new-hatched Tachi- 

 nid larvae, are sometimes covered with eggs of these parasites, while the softer 

 intermediate segments remain uninfested. 



Even when the larvae of Carcelia chelonae, referred to above, have pene- 

 trated the cuticle of the host, they may still be cast out by the ecdysis of the 

 caterpillar ; for they remain with their posterior spiracles in the entrance hole, 

 and while they are in this position, the hypodermal cells of the host proliferate 

 and secrete chitin so as to form a chitinous sheath round the parasite. This 

 sheath, with the contained parasite-larva, is sometimes moulted with the rest 

 of the cuticle of the host, or it may snap off and slip down into the body- 

 cavity of the host, where the parasite quickly perishes for want of air. 



The second article is a short note propoimding the question : How do 

 internal parasites resist the action of certain secretions of the host ? For 

 example, some Oestrid larvae live in the alimentary canal of mammals : at least 

 one Tachinid {Compsihira concinnata Meig.) passes its larval existence in the 

 intestine of its host ; other Tachinids, which oviposit on the food of the host, 

 pass their egg-stage in the alimentary canal, the new-hatched larvae boring 

 through the wall of the intestine into the body-cavity: the Hymenopteron, 

 Polygnotus minutus, passes its larval life in the intestine of Cecidomyia 

 destructor. How do such forms resist the action of the digestive juices ? It 

 has been experimentally shown by HoUande that the beetle Galerucella luteola 

 contains in its blood a toxic substance, which, when injected into the Carabid 

 Procrustes coriaceus, or into a lizard, rapidly causes death, yet a Tachinid 

 {Erynnia nitida) flourishes in the body-cavity of this very Galerucella, feeding 

 on the tissues and the toxic blood. 



The third paper is a pre! iminary note on the finding of a first-stage para- 

 sitic Dipterous larva (probably Dexiid or Tachinid) in the body-cavity of 

 another Dipterous larva {Sciara sp.). The writer states that he only knows of 

 two other cases' where one Dipteron has been found parasitising another 

 Dipteron One of these is the case of the Tachinid, Siphona cristata, parasitic 

 in the larva of the aquatic Tipula maxima. But whereas the Siphona-larva 

 attaches itself to the tracheal system of its host, the parasite here described 

 lies quite free in the body-cavity of the Sciara-larva, without any connection 

 with the tracheae. Possibly correlated with this is the fact that Thompson has 

 been unable so far to discover spiracles or tracheae in the parasite. 



The fourth article records the finding of first-stage larvae of an un- 

 determined Tachinid (one of tlxe Echinomyiinae) actually between the layers of 

 the chitinous cuticle of a Noctuid caterpillar (Hamemalis virginiana). The 



