October 1, 1894.] 



KNOWLEDGE. 



225 



chance of escape, and are easily gathered up as they fall. 

 Of course they must be killed in such a way as not to 

 damage their bodies, or in any way allow the valuable 

 substance with which they are impregnated to escape, 

 otherwise their commercial value would be impaired. 

 Hence they are kUled by means of a weak acid, either by 

 plunging them into vinegar, or by exposing them to the 

 vapour of acetic acid. The dead bodies, after being dried, 

 are then stored. 



But there are still difficulties to be contended with. As 

 is well known, the dead bodies of insects are a peculiarly 

 attractive bait to various small beetles, which are com- 

 monly known under the title of museum pests, and if 

 these once obtain a lodgment amongst a store of dried 

 Spanish fly, it is not an easy matter to dislodge them. It 

 is vain to hope that the internal doses of cantharidin 

 they are constantly administering to themselves by their 

 ravages will have any evil elt'ect, though this substance 

 when taken internally by vertebrates appears to act as a 

 dangerously irritant poison. When the museum pests 

 attack the stores of blister beetles, the amount of damage 

 done is measured simply by the matter actually devoured ; 

 for the cantharidin still remains uninjured in such parts 

 of the damaged bodies as may be left, and for medicinal 

 purposes it is by no means essential that the drinl bodies 

 should be perfect and entire, though, as we have already 

 hinted, it is desirable that when freshly collected, and 

 therefore moist, they should be in as perfect a condition 

 as possible, lest exudation of fluid, and therefore loss of 

 cantharidin, should take place. But the worst enemy to 

 be encountered is damp, which, though it does not dis- 

 integrate the bodies, yet does far more harm than the 

 above-mentioned devourers, since the characteristic pro- 

 perties of cantharidin are lost under its influence. 



Some insects are gifted with the peculiar power of 

 fashioning receptacles for their eggs, not out of extraneous 

 and foreign materials, which would nnply the exercise of a 

 certain amount of intelligence and ingenuity, but from 

 matter derived from their own bodies, and used in an 

 involuntary and unconscious way. Special glands exist 

 for this purpose, and open into the oviducts, so that the 

 receptacle is formed within the body of the parent, and 

 the insect never sees it till it is finished ; hence the eggs 

 are laid, not separately, but in sets, and, as it were, done 

 up in parcels. This peculiarity is specially characteristic 

 of certain groups in the order Orthoptera. In our own 

 country, the cockroaches aft'ord the best illustration of the 

 practice, but in the tropics excellent examples are to be 

 found in the various species of Mautidie, or praying insects. 



The egg-cases of the common household cockroach, or 

 " black beetle " of the kitchens, may often be fouad lying 

 about in the corners of cupboards, in houses where the 

 insect is plentiful. The case is a reddish-brown, horny 

 structure, about half an inch long, shaped something 

 like a lady's handbag, and containing, as a rule, sixteen 

 eggs, of which eight are placed on each side in perfectly 

 regular order, lying parallel to one another. The eggs, of 

 course, hatch within the case, and the young cockroaches 

 issue from their birth-chamber at its sharp edge, i.e., what 

 would be the line of opening in the handbag aforesaid, 

 where alone there is a junction. The material for these 

 cases is supplied by a special gland appended to the repro- 

 ductive apparatus, consisting of branched tubes, and called 

 the coUeterial gland, and the peculiar form is given to the 

 case by the chamber on the walls of which the secretion is 

 spread, and of which it therefore forms a sort of cast. 

 When the whole structure is completed and projierly 

 equipped with its complement of eggs, it is still carried 

 about by the mother for several days, during which time 



Fio. 18. — Egg-cise of a species 

 of Praying Insect attached to grass 

 stem. 



it may be seen protruding more or less from her body. It 

 is finally deposited in some safe position, unless the 

 ci-eature is alarmed, when she will sometimes drop it at 

 once. 



Our wild cockroaches similarly form cases for their eggs, 

 but as they are smaller than the domestic insect, the cases 

 are much smaller too, and naturally, each species has its 

 own peculiar form. Neat and shapely though these cases 

 are, they are much surpassed in elegance by those formsd 

 by the exotic Mantitla. 

 These are large and pre- 

 daceoiTS insects with long 

 and powerful fore-legs, 

 which, when watching for 

 their prey, they hold in 

 front of them in the position 

 that has been suggestive 

 of an attitude of devotion, 

 whence the name " praying 

 insects," sDmetimes applied 

 to them. The egg-receptacles of these insects (Fig. 18) 

 are made of a clear, shining, pale yellowish substance, 

 which is thin and semi-transparent, so that they look as if 

 made of varnished paper or membrane. The surface is 

 indented with a delicate tracery of reticulations, which 

 throw it up into a series of minute rounded elevations. 

 The cases are not left lying about on the ground, but are 

 fastened by a little loop at the lower end to the twigs of 

 trees and the stems of grasses. 



The principle of construction is much the same as in the 

 cockroach-bags, and so far as external appearances are 

 concerned, may be paralleled, if one may borrow a familiar 

 illustration from the pastry-cook, by that of the old- 

 fashioned " apple turnover." As in that article of diet 

 there is a cover whose continuity is unbroken save along 

 a line on one side, where the two edges have been pressed 

 together, and as the ingenuity of the cook seems often to 

 have been expended in crimping and otherwise ornamenting 

 the rim at this line of junction, so we find in the Mmiti.-t 

 cases a raised line where the two edges meet, and a very 

 pretty row of markings along it. Within, a partition, 

 which looks as though made of congealed froth, ruas 

 across from the line of junction towards the opposite 

 surface, but without reaching it, and the eggs are placed 

 in regular order on each side of that partition, so that they 

 are back to back, and remind one of the arrangement of 

 the cells in a honeycomb. 



It is an obvious suggestion that the purpose of these 

 receptacles is to protect the eggs from hymenopterous 

 parasites, many of the minuter forms of which are quite 

 satisfied with the contents of a single egg-shell as the totil 

 provision for their larval life, so that they pass through 

 their early stages parasitically within the eggs. But that 

 the cases do not always accomplish this purpose appears 

 from a specimen now before me, in which many of the 

 eggs have been devoured by parasites, some of which have 

 reached their perfect condition, and their shining metallic 

 green bodies are still to be seen amongst the remains of 

 the eggs to testify to the fact of their former ravages. 



Taking now a brief mental review of the numerous and 

 varied facts we have described in this series of papers on 

 " Insect Secretions," we may point out one or two general 

 conclusions to which they seem to lead. In the first place, 

 we have the fact that during the lifetime of many insects 

 there occurs a period in which the creature becomes quite 

 helpless, not simply by passing into a torpid condition or 

 a condition of suspended animation, but by the actual 

 loss of its limbs, and with them the power of locomotion 

 and therefore of escape from danger, and by the abortion 



