THE GENUS ACRONYCTA AND ITS ALLIES. 147 



be entirely green, but usually retains a black spot on either 

 side, the plates on the sides of the legs are black, the spiracles 

 orange ; the head is small and the larva tapers to either end 

 and continues remarkable for transparency, displaying trachea 

 and other items of internal anatomy. 



The larva always rests underneath the leaf, and as soon as 

 large enough, along the mid-rib, and when full-grown along the 

 central petiole of the ash leaf, which is its usual food. The 

 tapering to either extremity assists it in eluding observation 

 when so placed, indeed it is rather difficult to see, notwith- 

 standing the bulk of the full-grown larva, and a half-grown one 

 may be easily overlooked, even when changing the food in 

 captivity, although its presence is of course well known. 



I do not know, from personal observation, where the cocoon 

 is made naturally, never having met with one ; but my friend, 

 the Rev. G. M. A. Hewett, finds that they make them under 

 moss on the trunks of the ash trees, when such a situation is 

 available. In captivity, some individuals ascend, and like to 

 spin under some overhanging ledge, but the majority appear to 

 prefer to go downwards and spin among dead leaves and 

 surface rubbish, generally against the side of cage, however, 

 and, probably, they usually spin against the stem of the tree. 

 The cocoon consists of very dark, nearly black, silk, and is of 

 considerable strength, in one dense layer, without any admixture 

 of chips or extraneous matter, but adhering, if possible, to 

 some leaf or other object all round. This habit makes it of 

 varying and irregular form, and so gives rise to a little doubt 

 whether the fact that the point of exit is usually a valvular slit 

 is a true and constant result of instinct, or is due to this point 

 being so often where two objects, between which the cocoon is 

 made, meet at an angle. The fact, however, is undoubted, that, 

 unlike Viminia with a weak place in the cocoon, or Cuspidia 

 with a specially-arranged, but not specially weak point of exit, 

 Bistdcia ligustri has frequently a valvular slit in the cocoon, 

 often nearly as completely elaborated as in Hylopliila or Saro- 

 thripa. 



The pupa (PI. I., fig. 3, and PI. IV., fig. 4) is even more 

 distinct from those of Viminia and Cuspidia,\h^.n they are from 

 each other. Having only one species to deal with, it is difficult 

 to take any of the points of difference as being generic rather 

 than specific, but, as a provisional expedient, it is perhaps 

 simplest to regard them all as being so. It is of the Noctua 

 type as regards general appearance and texture, short and 



