JuLT 2, 1894.] 



KNOWLEDGE. 



147 



is the most extraordinary difference between tbe adult 

 male and female insects. They are. to begin with, all 

 small creatures, some very minute. The males are pro- 

 vided with a single pair of wings, which in itself is an 

 exceptional circumstance, since they belong to an order — 

 the Homoptera — the members of which are normally four- 

 winged. Thus they remind us of the two-winged flies, or 

 Diptera, and the suggestiveness of their appearance is 

 strengthened by the fact that they possess a pair of short 

 hooked appendages where we might expect hind wings, by 

 which we are at once reminded of the "balancers" of flies. 

 Nevertheless, their general aspect is so difterent from that 

 of the majority of dipterous insects, that they are hardly 

 likely to be mistaken for members of that order, especially 

 as they usually carry a pair of long bristles as a sort of tail. 

 (See accompanying plate.) 



In the organization of these little males everything is 

 sacrificed to the one purpose of their life, that of re- 

 production, and such other functions as may be more or 

 less accessory to that, as, for example, sight and locomotion. 

 Thus we find that the mouth organs 'are atrophied, the 

 digestive apparatus shrivelled up, and that part of the 

 body which usually lodges the stomach and intestines 

 contracted to very small dimensions. They take no food, 

 and necessarily, therefore, Uve but a very short time. On 

 the other hand, they have an excellent supply of eyes, the 

 usual masses at the sides of the head being supplemented 

 by two large additional eyes on its upper surface, and this 

 superabundance of the means of sight must be of consider- 

 able advantage in their search for inates. They are 

 themselves not so well known as their partners, and in 

 many species have not yet been discovered at all. As a 

 consequence, it is evident that parthenogenesis must 

 frequently take place. 



The fully-grown females are about as different as could 

 well be imagined. They have no power of flight — nor, 

 indeed, of locomotion of any kind, for in their adult form 

 everything is sacrificed to the nutritive and reproductive 

 functions, since they are destined to be great feeders and 

 mothers of large families. As they are not required to go 

 in search of mates, but enjoy the honour of being them- 

 selves sought out, and have nothing to do but wait to be 

 wooed and then settle down to their maternal functions, 

 means of locomotion and organs of sense are alike super- 

 fluous. Accordmgly we find that antenna and legs all 

 ultimately disappear, while the mouth organs become 

 highly developed, the piercing beak being sometimes six 

 times as long as the rest of the insect. When fully grown, 

 they seem to be little more than minute, inert lumps of 

 flesh, the animal nature of which is by no means obvious 

 to the naked eye till they are crushed. 



The difierent species have the power of secreting 

 materials of various kinds, which, on exuding from their 

 bodies, form in most cases variously shaped scales, under 

 which the insect is to be foimd. The " mussel-shells " 

 mentioned above are examples of these scales. There are 

 many diff'erent species, and their scales are of varied forms 

 and colours, the majority being more or less oval or linear. 

 Those that will produce males are both dift'erently shaped 

 and differently coloured from those that will develop into 

 females. They are often found on the leaves as well as 

 the branches of plants, each species having its own distinct 

 kind of food-plant. One very common species which proves 

 itself a great pest in conservatories is found on the under 

 side of the leaves of the oleander, especially along by the 

 side of the midrib, where it forms oval, convex, orange or 

 brownish scales. It is from these scale-like coverings 

 that this particular section of the Hnraoptera have been 

 called " .scale-insects." 



The glands by which the material of the scales is 

 secreted lie, according to Mr. A. Morgan, on the upper 

 surface of the hinder part of the abdomen, and are some- 

 times very numerous ; they are tubular, and open by small 

 pores in the skin. The exudation from them is of a very 

 varied character. Sometimes, as we have seen, it forms a 

 distinct scale, which shelters the insect beneath ; some- 

 times it is in the form of cottony or silky threads, which 

 may remain adherent to the body, or may be deposited 

 as a covering for the eggs. Or, again, it is of a waxy 

 nature, as is the case with the maker of the Chinese insect 

 wax of commerce, a species of Coccus nourished on a kind 

 of ash tree. The insects that form this secretion suck up 

 the sap of the tree to such an extent that they ultimately 

 become almost entirely converted into masses of wax, 

 which encrust the branches. This wax, when separated 

 from the branches, is melted over a slow fire and then 

 poured into cold water, by which it is washed and at the 

 same time solidified into flakes. These are again melted 

 and cast into cakes, and the wax then appears as a hard, 

 translucent, crystalline substance, something like sperma- 

 ceti. It is used for a variety of purposes in the East, 

 especially for making candles and in the practice of 

 medicine. It must be carefully distinguished from Japanese 

 wax, which is also used for candle-making, but is a 

 purely vegetable product obtained direct from the fruits of 

 certain trees, and not elaborated from plant juices through 

 the medium of an insect's digestive and secretory apparatus, 

 as is the case with the Chinese product. 



Several other of these Cvccida yield valuable products, 

 of which they are either directly or indirectly the origi- 

 nators. For example, the splendid scarlet dye called 

 cochineal is derived from a species which is cultivated on 

 cactus plants in Mexico, Madeira and elsewhere. The 

 wingless and legless bodies of the female insects are 

 collected and dried, when they look something like seeds ; 

 and from these the dye is obtained. The substances 

 called " lac " and " manna," again, are produced as 

 exudations on certain trees by the punctures of other 

 species of scale-insects, the former on a kind of fig tree 

 and the latter on tamarisk. The lac, while still adhering 

 to the branches, is called stick-lac, but after separation 

 and various degrees of refinement it is known by the names 

 of seed, lump, and shell lac, the latter being the form in 

 which it is most familiar to the British public. 



The life-history of insects belonging to this group is 

 generally somewhat as follows. The young larvs, when 

 just hatched, are furnished with the usual insect appur- 

 tenances, and are more or less active ; but they soon 

 attach themselves to the leaf or bark, become modified in 

 form, and begin to grow a scale. The female casts its 

 skin twice, but the male only once. The cast skin is to 

 be seen either in the centre or at one end of the scale, 

 fastened there by the secretion of which the scale is 

 composed. After a time, the insect changes into a 

 chrysalis, which again is peculiar, for the rest of the 

 Homoptera do not exliibit a complete metamorphosis, but 

 are active throughout life. The female deposits her eggs, 

 which are numerous, under the scale, just behind her own 

 body, and having done this she dies, leaving her shrivelled 

 body just where it was. The adult insect is often much 

 smaller than the larva which yielded it, and this shrinkage 

 of course leaves room for the eggs and young insects under 

 the scale, until the latter leave the parental roof and settle 

 down elsewhere by pushing their beak-bristles into the 

 plant as a permanent anchor and suction apparatus. 

 Sometimes there is not only the rounded scale on the 

 insect's back, but in addition to this a flat one, very much 

 thinner than the other, is formed underneath the body. 



