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spines are sometimes found between the girdles of spines 

 (Figs. 46,63). In the first stage of Steiniella callida (Figs. 

 54,64) and in the third stage of Ocyptera brassicaria (Fig, 

 60) there are chitinous plates in the integument. 



With regard to the detailed descriptions of the larvæ 

 I may refer to the Danish and to the explanations of the 

 figures. 



2. Biology. 



The relation between the hosts and the parasites is 

 nearly the same in all the examined species parasitic on 

 insect-larvæ. As type I have dealt in detail with Ptycho- 

 myia selecta Meig., a species which is parasitic on the full- 

 grown larva of Hyponomeuta euonymella Scop. The fly 

 deposits its eggs in June and July irregularly on the body 

 of the host in a number of from 1 to 23. ^) The parasites 

 penetrate from the eggs directly through the integument of the 

 host larva (Fig. 47). This gives rise to an invagination of 

 the cuticula of the host round the margin of the hole of 

 entrance (Fig. 1,2); the invagination forms a funnel (Fig. 

 47) that encloses the posterior end of the larva which 

 respires through it. On the outside of the chitinous funnel 

 is found a coating of hypoderm-cells (Fig. 2 ep.). The chi- 

 tinous funnel is continued by a sac-like layer, quite enclo- 

 sing the parasite (Fig. 1 s). This sac consists of fat-cells, 



^) It is very common to find on the hosts of the parasitic flies a 

 considerably greater number of eggs or more or less young larvæ 

 than the host can support. The parasites thus penetrate into 

 the host, but a greater or smaller number die at an earlier or 

 later stage of development. The death is sometimes caused by 

 pressure from the other larvæ, but cases are commonly found in 

 which the death has not arisen from mechanical power from the 

 side of the other larvæ. Similar cases occur also in other para- 

 sitic insects (cf. p. 95 — 100 and the literature here cited.) 



