436 LECTURE xvin. 



not essential ; they relate to the place in, and the time during, which 

 the metamorphoses occur, and to the powers associated with particular 

 transitory forms of the insect. The legs of the worm-like embryo- 

 locust were once unarticulated buds, like the prolegs of the caterpillar ; 

 but the creature was passive, and development was not superseded for 

 a moment by mere growth ; these organizing processes go on simul- 

 taneously ; or rather, change of form is more conspicuous than increase 

 of bulk. The six rudimental feet are put to no use, but constitute 

 mere stages in the rapid formation of the normal segments, which 

 attain their mature proportions, and their armature of claws and 

 spines, before the egg is left. The first segment of the original apodal 

 and acephalous larva is as rapidly and uninterruptedly metamorphosed 

 into the mandibulate and antennate head, with large compound eyes. 



Thus developed, the young Orthopteran or Hemipteran issues forth 

 into active life. Instead of further individual improvement or de- 

 velopment, it may at once begin the great business of its existence 

 by parthenogenetic propagation of its kind, as in the Aphis, and feed 

 and die without further change of form ; but, generally, the active, 

 crab-like larvas are subject to three moults. After the first the larva 

 has merely increased in size ; but the rudiments of the wings begin 

 to bud forth beneath the second skin ; and, after the second ecdysis, 

 they present themselves externally as small leaves, which cover the 

 sides of the first abdominal segment. When this active pupa or 

 nymph again moults, the insect attains its perfect condition; the, at 

 first, short, soft, and thick wings rapidly expand to their full size, 

 then dry in the air ; the circulation of the blood along the nervures 

 is arrested, and the metamorphosis of the individual is complete. 

 Here, then, we see that the pupa stage, which, in the butterfly, was 

 passive and embryonic, in the locust is active and voracious ; whilst 

 their respective conditions in the larval state are reversed. The 

 whole period of the life of the Orthopterous insect, from exclusion to 

 flight, may, if its organization during that period be contrasted with 

 that of the Lepidopterous or Coleopterous insects, be called an active 

 nymph-hood. 



Entomologists, overlooking that stage of the Orthopterous and 

 Hemipterous insects, in which they are masked by the vermiform or 

 true larval condition, have arbitrarily applied the term " larva " to 

 the more advanced stage in which these insects, with certain Neurop- 

 tera, quit the egg. Mr. Westwood seeing that at this stage they are 

 nearly similar in form to the perfect insect, though wingless, has 

 proposed to call them " homomorphous," or " monomorphous ; " and 

 those insects in which the larva is generally worm-like, &c., hetero- 

 morphous. It needs only an acquaintance with the embryonic changes 



