November 1, 1898.] 



KNOWLEDGE. 



217 



had to be appealed to, for the moth, not having sufiScientl}' 

 strong mechanical means to free itself from its prison, 

 invokes the aid of chemistry. Mr. Oswald Latter removed 

 some pup:i> from their cocoons shortly before their emer- 

 gence, and wrapped each np in a piece of the thin blotting 

 paper used by chemists for filtering solutions. Each, 

 therefore, on becoming a moth, had to pierce the paper 

 instead of its cocoon. As this took place, it was found 

 that the paper was wetted at the spot of emergence, a stain 

 being left behind when it dried. By using a number of 

 these stained papers, enough of the material which com- 

 posed the stains was procured to enable an analysis to be 

 made. It was then found that the liquid, which was 

 evidently poured out by the moth at the time of its emer- 

 gence, was none other than that very well-known substance, 

 caustic potash, renowned and widely used for its solvent 

 powers. This was a very interesting discovery, for it had 

 not previously been know'n that any animal secreted a 

 caustic alkali ; moreover, it was doubly interesting from 

 the fact, to which we have previously referred, that the 

 caterpillar of the same moth secretes a liquid of a chemi- 

 cally opposite character, viz., formic acid. The next step 

 was to try whether the material of the cocoons was soluble 

 in caustic potash. A few drops were placed on the inside 

 of some cocoons, and in three minutes they were reduced 

 to a pulp. Here, then, stood revealed the means by which 

 the creature was able to effect a breach in its strong prison 

 walls ; it actually dissolved its way out by means of a 

 caustic alkali. 



But the explanation was not yet quite complete, for if 

 the alkah were the only means of egress used, it seemed 

 likely that there would result a general softening of a part 

 of the wall of the cocoon, and a bursting out through that, 

 rather than, as was really the case, the neat separation of 

 a portion of the wall, the severed piece remaining as hard 

 as the rest. The moth was found to make its exit wearing 

 a sort of cap, consisting of the front part of the chrysalis 

 shell, which fitted on to its head by means of little pro- 

 jections and sockets, and served as a shield, protecting the 

 underlying parts from damage during the 

 passage out. Close examination revealed 

 just beneath this shield a couple of hard 

 sharp points projecting from above the 

 moth's mouth, and usually concealed by 

 the fluffy down around. These are the 

 instruments by which the section is made, 

 though they would be quite powerless if 

 the silk were not first moistened and 

 softened by the secretion. Thus the moth 

 is most wonderfully armed for burrowing 

 its way out ; with a shield on its head, 

 two diggers beneath, and a supply of alkali 

 to overcome the resistance of the wall 

 it has to penetrate. 



When cocoons are attached to grass 

 stems, they naturally tend to become 

 shuttle -shaped ; the stem runs up one 

 side, and the ends of the cocoon taper 

 away till they are reduced to the thick- 

 ness of theu' support. Two very good 

 instances of this are to be seen in the 

 " di-inker " moth and the family of 

 burnet moths. The caterpillar of the 

 " drinker " (i hlo»<-st>s potatorui) is a hairy creature, with 

 two extra long and close tufts of black hairs like 

 horns, one at each end, and also with a number of short 

 snow-white and deep yellow or orange tufts along the 

 sides. It feeds on grasses, and has the habit, when 

 disturbed, of dropping to the ground and rolling into a 



!J. 



.1 



Fig. 3. — Coeoou 

 of Driutei- Motli, 

 on grass stem. 



very compact ring. The moth is coloured something like 

 the oak-egger, but is not so large; nevertheless, the cocoon 

 (Fig. 3) is a good deal larger. It is of a pale yellowish 

 colour, leathery and flexible, and thus quite imlike those 

 we have just been considering. It has a slightly irregular 

 and crumpled appearance outside, but inside is smoother, 

 although the individual silken threads can be much more 

 distinctly traced here than outside, where the texture looks 

 more irregular and matted. Some of the caterpillar's 

 hairs are worked into the structure outside. 



The burnet moths are extremely brilliant insects, which 

 frequent grassy hill-sides and meadows, and delight to 

 fly in the brightest sunshine. There are several kinds, 

 but they are all narrow-winged moths, with long stout 

 bodies ; the forewings are of a brilliant metallic greenish- 

 black, adorned with crimson spots, and the hind wings 

 are rich crimson with a black border. The commonest 

 species [Xijiiinui rilijienduhr) has si.v crimson spots on the 

 fore-wings, and is an abimdant and well-known insect in 

 suitable localities. The cocoons of these creatures are of a 

 shining golden colour, thin and papery in consistence, but 

 nevertheless harder and more unyielding than that of the 

 "drinker,' as well as much smaller. They are usually 

 attached to grass stems, and three or four are sometimes 

 placed on the same stem (Fig. 4), either one above the 

 other or clustering round at the same level, and therefore 

 more or less overlapping one another. Their bright 

 colour and elevated position makes them 

 very conspicuous objects. Occasionally 

 the cocoons are constructed in other 

 places, such as on fern fronds, thistle 

 stems, or even stones, but the grass stem 

 is the general rule — a rather curious 

 association, since grass is not, as it is with 

 the " drinker," the food-plant. 



There is no ditfioulty in telling whether 

 the insect is within or not, for when it 

 escapes it leaves the front half of the 

 empty chrysalis case sticking out of a hole 

 in the cocoon, and the contrabt between 

 the black shell and the golden vase which 

 supports it is very striking. This position 

 is assumed by the chrysalis before the 

 emergence of the moth, whence it is 

 evident that, though limbless, it has the 

 power of climbing ; the means of doing 

 this consist of rows of minute hooks on 

 the segments of the abdomen, just as 

 with the leaf-rollers we described on a 

 former occasion. In this habit the burnets 

 are quite unlike the other insects we have 

 referred to, which, as they ha%'e no hooks 

 and cannot climb, all leave their empty 

 shell wholly inside the cocoon. Another 

 difference is that the cocoon is simply 

 burst open at the end, and no part of it 

 is actually separated from the rest. But 

 here again we find a resemblance to the 

 " drinker," which does the same ; and 

 since in this case the chrysalis skin does 

 not project, and the cocoon is scarcely 

 damaged by the escaping moth, it is not an easy matter, 

 except by the touch, to decide whether the cocoon is 

 empty or full. Neither "drinker'' nor burnets require the 

 accommodation of the cocoon for more than a few weeks at 

 the outside, and when once they are broken open and 

 deserted, the weather soon makes them more and more 

 dilapidated, and they are not long in going to ruin. 

 (To be continued.) 



Fiff. 4. — Four 

 Cocoous of Bur- 

 net Ifoth , on grass 

 stem, the empty 

 chrvsalis cases 

 projecting. 



