1892. J 171 



hinder part of the back of 12th segment; it is not always present, nor equally dis- 

 tinct when present ; it is not a plate, and disappears along with the loss of colour 

 that takes place during the latter weeks of hibernation, whereas the plates at that 

 time show up more cleai'ly by contrast. 



The figure in Nat. Hist. Tin. shows four faint grey marks on the 

 back of 4th, where the plates should be found. They are not, how- 

 ever, true plates, but only slight grey stainings of the skin, of very 

 uncertain occurrence, and are always lost, 1 believe, before the larva 

 has done feeding. The absence of the dorsal plates on 4th, and the 

 presence of the dark mark on 12th, are important points, for they 

 are the distinguishing characters of this larva. It becomes full-fed 

 in the autumn, when it leaves the rush-heads, and hides away in the 

 surrounding vegetation. Its favourite foods here are J. conglomeratus 

 and effusus. I have also found it on lamprocarpus (not commonly), on 

 squarrosus, as already stated (freely), and on glaucus (rarely). It is, 

 no doubt, because the last named rush is distasteful to it, and at the 

 same time monopolizes the fields and lanes in these parts to the ex- 

 clusion of conglomeratus and effusus, that ccBspititiella is driven in my 

 district into the woods. Mr. Bankes has sent it me on J. compressus, 

 and Mr. Fletcher on acutiflorus ; and probably it feeds on other kinds 

 as well. 



The case is so well known that it would be superfluous to de- 

 scribe it, yet there may be room for a few remarks on the mode of 

 its construction. In the first place, the larva is later than any of its 

 fellows in beginning its case. I have not, however, ascertained the 

 precise date, and am inclined to think that the larva is bound by no 

 hard and fast rule in the matter, but sometimes sets about it just 

 before the last moult, and sometimes not till after that event. As 

 this would be an exception to the general law that a change in the 

 habit or economy of a larva, or even any definite act performed by it, 

 such as exchanging a small case for a larger one, coincides with a 

 definite point in its age, it is possible that further observation may 

 show that the above conclusion is incorrect. But be this as it may, 

 the larva is long past its babyhood when it begins to build. The case 

 makes it first appearance aa a short and stout cylindrical tube, pro- 

 jecting through the gap in the capsule, caused by the natural 

 dehiscence of the valves, or else through an artificial opening cut by 

 the larva itself. It is thin and flimsy, semitransparent, and covered 

 with minute brown fragments of vegetable debris, and has the outer 

 or anal end blunt and rounded, and, strange to say, closed. After 

 some delay, the tail end is gradually built out, a triquetrous shape 



