the second instar has a soft cuticle and relatively shorter legs, which, as the larva, now living as a cuckoo-parasite, proceeds to gorge itself with honey, soon appear still further abbreviated.  Later comes a stage during which legs are entirely wanting, the larva then resting and taking no food.  The last larval instar again has short legs like the grub of the second period.  In connection with this life-history we notice that the newly-hatched larva is not in the neighbourhood of its appropriate food.  Hence the preliminary armoured and active instar is necessary in order to reach the feeding place; this journey accomplished, the eruciform condition is at once assumed.

In all cases indeed we may say that the particular larval form is adapted to the special conditions of life.  A few examples from other orders of endopterygote insects will illustrate this point.  The campodeiform type is relatively unusual, but most of the Neuroptera have larvae of this kind, active, armoured creatures with long legs, though devoid of the tail-processes often associated with similar larvae among the Coleoptera.  Such are the ‘Ant-lions,’ larvae of the exotic lacewing flies, which hunt small insects, digging a sandy pit for their unwary steps in the case of the best-known members of the group, some of which are found as far north as Paris.  In our own islands the ‘Aphis-lions,’ larvae of Hemerobius and Chrysopa, prowl on plants infested with ‘green-fly’ which they impale on their sharp grooved mandibles, sucking out the victims’ juices, and then, in some cases, using the dried cuticle to furnish a clothing for their own bodies.  Among these insects, while the mouth of the imago is of the normal mandibulate type adapted for eating solid food, the larval mouth is constricted and the slender mandibles are grooved for the transmission of liquid food.

Turning to eruciform types of larva, we find the caterpillar (fig. 1 b, c, d) distinguished by its elongate, usually cylindrical body with feeble cuticle, short thoracic legs and a variable number of pairs of abdominal pro-legs, universal among the moths and butterflies forming the great order Lepidoptera, and usual among the saw-flies, which belong to the Hymenoptera.  The vast majority of caterpillars feed on the leaves of plants and their long worm-like bodies with the series of paired pro-legs, are excellently adapted for their habit of clinging to twigs, and crawling along shoots or the edges of leaves as they go in search of food.  Of great importance to a caterpillar is its power of spinning silk, consisting of fine threads solidified from the secretion of specially modified salivary glands whose ducts open in the insect’s mouth at the tip of the tubular tongue which forms a spinneret.