242 MISS A. L. EMBLETON ON THE ANATOMY 



Encyrtus fuscicoUls the tracheae of the host ramify on tlie tube containing the parasite, 

 and serve for respiration of the young Encyrtus. The only other case I can fiud bearing 

 on this point, is that described in 1S37 by Dufour, of Andrena uterrima and a parasitic 

 Dipterous larva*. Dufour claims that two of the host's tracheae grow into the body of 

 the larva, which is thus supplied with air ; bvit there seems some doubt about the inter- 

 relationship in this case. 



As this instar passes into the next, the posterior pair of external tracheae become 

 marked by the appearance of three red-brown plate-like structures on each side of the 

 l)ody of the larva (PL 11. figs. 16, 17, 18, ^^Z.) ; they are situated at the point where the 

 radiating external tracheae are united Avith the body-wall. These curious plates are 

 present in the pupal condition, but are left behind M'hen the pupal skin is cast. 



Thus we see, in summarizing the facts recorded above, that in the larval condition 

 respiration is at first carried on by means of a bif arcated tail-apparatus in which the 

 two lateral tracheal trunks are continued ; in this condition there are no spiracles, but 

 later on the two tapering tails atrophy, and spiracles are developed. Tliis condition is 

 superseded by an arrangement of tracheae ramifying outside the parasite, in the body of 

 the host ; there are now 8 pairs of stigmata, and the posterior pair of radiating tracheae 

 arise in the 9th segment behind the head. 



Before the next (or prepupal) instar is reached, a process of histolysis takes place by 

 which the internal organs arc completely broken down, to be built up into the pupal 

 tissue by means of a process of histogenesis, or regeneration. 



In this instar, or at any rate during the later period of its existence, the larva appears 



to possess a membranous coat, or sheath. It is to a membrane of some kind or other 



that Bugnion refers in the passage quoted above as to the respiration of the larva of 



Encyrtus fuscicolUs : he states that the embryos are all in one long common capsule, 



and he is of opinion that this is a product of the egg ; but the case diifers so widely from 



that of Comys infelix, that his facts cannot be of much service in making a parallel 



argument. As to the nature and origin of this sheath in Comys infelix, I am quite in 



doubt. Subsequently, as we shall see in the next instar, there exists a well-defined and 



ample membranous sheath, but whether the membrane observed in the third instar is 



really the same as that found later, or not, I cannot say with any certainty ; no actual 



ecdysis has, however, been observed, and I think it is probable that the sheath is a 



larval skin retained on account of the respii-atory apparatus attached to it externally. 



The question is complicated by the appearance in the next (or prepupal) instar, at the 



base of this respiratory aj)paratus, of additional structures in the form of certain oval 



red plates (PI. 11. figs. 16, 17, 18, pi.), which appear to be applied to the sides of the 



body at the spot where the tracheae radiate out. If these were developed outside an old 



skin, it would be a very remarkable fact : I have alluded to the possibility that these 



respiratory structures are really formed by the host, and in that case there would be no 



difficulty in understanding that they undergo further develojiment even on the separated 



skin of the parasite. 



* Cf. Cambridge Natural History, Insects, ii. (D, Sharp), p. 26, fig. 13. 



