AcanfhopsT/chc ojxicdla. 407 



pupal case being shoved back on the retreat of the moth 

 into it. 



The hirval sac is a tube alonir which the larva and 

 male pupa can travel to and fro with facility, so could the 

 female pupa were it not fixed in this way and by the 

 exserted intersegmental dorsal spines. But the female 

 moth is in a ditferent position, the tube along which it 

 has to travel is not the larval sac posteriorly, but the 

 empty pupa case ; anteriorly the larval sac does not 

 correspond with this, but is of course considerably larger 

 just at the anterior end of the pupa. The silken mesh or 

 hammock (partial) we are considering, just bridges over 

 this space, and so proves a guide to the female in her 

 retreat to the pupa case, preventing her from missing the 

 opening, which otherwise she would be tolerably certain 

 to do, as well as preventing her pushing it back behind 

 her instead of entering it. It would be still more impos- 

 sible for the male moth to find this opening, even assuming, 

 as is probable, that he keeps more or less in touch with 

 the female whilst she retires ; that he does not always so 

 keep in touch is also however probable, as pairing takes 

 place, even when the female is not at the opening of the 

 sac on the arrival of the male. 



This silk mesh must have a definite valvular structure, 

 admitting of the moths finding an easy tubular road 

 through it, and yet closing up when they are not using it. 

 It must therefore of itself present some valuable protection 

 against the entry of enemies, against which the moth first, 

 and afterwards for some weeks her eggs, require protection. 

 It is probably largely in aid of this function that the struc- 

 ture is so effectual in rubbing otF the woollen clothing of 

 the moth. So effectual is it that in a very short time, a 

 moth having made a few journeys through it to and fro, 

 becomes quite denuded and presents the usual appearance 

 of a bare maggot. The great mass of the hair remains in 

 this position, that which escapes from the mouth of the 

 sac and that that gets distributed amongst the eggs, being 

 trivial in amount and apparently accidental. 



In some large exotic species a large mass of these hairs 

 occurs at this position, and even in A. opacdla the amount 

 is very considerable, much greater when teased up than it 

 appeared when dispersed in orderly fashion on the moth. 

 On first opening a female case containing eggs it is rather 

 difiicult to distinguish this hair from the silken net that 



