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The position of the Rhipiphorus-larva. inside that of the wasp, when it 

 is ready to emerge, is with the head to the point of emergence at the front of 

 the fourth segment, with its body extending into the flanks of the second 

 and third segments, and its ventral surface towards the skin of the wasp. 

 The larva; that I found in the still feeding wasp-grubs were clearly in the 

 general cavity of the body of the wasp, among its fat-masses, &c, and not, as I 

 imagined might be the case when I had only seen them in spun-up grubs, be- 

 tween the larval and pupal skins of the host. I may mention that when the 

 young Rhipiphorus has emerged, the black markings of its cast skin are always 

 easily detected in front of the fourth segment. All that I allowed to do so 

 emerged within four hours of the taking of the nest ; and, to take a round num- 

 ber, it seems probable that they do so within six hours of the spinning-up 

 of the wasp-grub. This idea is confirmed by the fact that though all the 

 still infested grubs had the dislocation of the larval head that occurs so soon 

 after spinning-up, some had no trace of the pupal eyes, and others -but a faint 

 brown mark. I have described the Rhipiphorus-\z.w& in this stage as being 

 4i millims. in length, and I find I have notes of larvae feeding outside the wasp 

 of less than 3 millims. On emerging, the larva becomes shorter and thicker, 

 and very soon loses length by that curving forwards of its head which is so 

 marked in thefull-grown larva, and which does not exist before its emergence. 

 The young larva of Rhipiphorus is now found lying like a collar immediately 

 under the head of the wasp-grub, and is attached to it by the head, though 

 not very firmly. At this stage the feeding of the young Rhipiphorus is rather 

 sucking than eating. In the case of a larva 4 millims. in length, the wasp grub 

 was rather flaccid at the upper extremity; one of the pupal eye-marks had 

 disappeared ; yet there was no wound of any size in the skin, though very slight 

 pressure caused fluid to exude. When we examine the mouth-apparatus of the 

 Rhipiphorus-laxva., we see that, though it must make a wound in the skin, its 

 jaws are ill-adapted for anything like eating. As the Rhipiphorus-hrva, grows, 

 its hinder segments pass downwards in front of the wasp-grub, and its mouth 

 retains hold of the upper extremity of the was-grub. When it has grown 

 to a length of about 6 millims. it casts its skin for a second time ; and, so far aa 

 I have been able to observe, it only does so twice (the first time was on emer- 

 gence from the wasp-larva). The skin splits down the back, and remains 

 attached to the front of the larva, lying between it and the wasp. When the 

 Rhipiphorus has grown as large as the diminished wasp-grub, the latter, par- 

 tially eaten (for by this time some of the skin has disappeared), easily accom- 

 modates itself to the other occupant of the cell ; and about this period the 

 curving forwards of the head of the beetle-larva, hitherto well-marked, becomes 

 extreme. Although there is still a good deal of wasp to be eaten, the cell from 

 above (in natural position, of course, below) shows only the back of the thoracio 

 segments of the Rhipiphorus-Xa.rva., the remains of the wasp lying in the space 

 formed by the flattened front of the Rhipiphorus, from the sixth to the eleventh 

 segments (Figs. 5, 6, 7). So far as tolerably close observation enables me to say, 



