December 19, 1895] 



NATURE 



155 



a forceps. Campodea and Japyx have no eyes, but this 

 is not considered typical ; simple eyes are usual in insects 

 of the same grade. They undergo no metamorphosis. 



Brauer finds forms closely resembling Campodea 

 among the larvie of Orthoptera, Perlida;, Odonata, Ephe- 

 meridas, Coleoptera and Neuroptera. In Strepsiptera and 

 Coccidae he considers that they are present in a more 

 modified form. No Campodeiform larvx occur among 

 Lepidoptera, Hymenoptera, or Diptera. 



Brauer looks upon the caterpillar of Lepidoptera, 

 Sawflies and Panorpa as a degenerate Campodea, while 

 he considers the apodous maggot of many Coleoptera, 

 some Neuroptera, Bees and Muscidas as a still more 

 degenerate larva, derived from, and not historically 

 antecedent to, the Campodea. Grassi and others have 

 brought forward facts to show that the maggot-like Bee- 

 larva has previously passed through a kind of Campodea- 

 stage. 



Lubbock regards the caterpillar too as essentially a 

 Campodea. But this extension seems to me to take all 

 definiteness out of the Campodea-form. If every larva 

 with biting mouth-parts and six legs is to be called a 

 Campodea, we still want a name for the larva which has 

 long legs, long antenniie and at least one pair of abdominal 

 appendages. 



Brauer's Campodea seems to invite comparison with 

 Scolopendrella and Peripatus ; just as the. more generalised 

 Campodea of Lubbock invites comparison with the 

 hexapod larva of Diplopoda and Atax. I do not venture 

 to pursue these comparisons, which involve difficulties 

 not apparent at first sight, and will only remark that the 

 former comparison seems to throw most light upon the 

 phylogeny. The leg-bearing segments of the Diplopoda 

 are apparently not the same as those of insects, and the 

 embryology of insects points to a polypod, rather than to 

 a hexapod, as the common ancestor of the Tracheates. 



If it seems rash, with our present knowledge, to trace 

 the phylogeny of Peripatus, the Myriopods and the 

 insects, what shall we say of Lubbock's far bolder attempt 

 to derive his Campodeiform larva from a Rotifer-like 

 ancestor.'* It is suggested, though not positively asserted, 

 that certain apodous dipterous larvie exemplify this 

 earlier stage. I must declare myself altogether sceptical 

 as to a Lindia-stage antecedent to the Campodea. The 

 only apodous insect-larva; known to me are bom of 

 highly specialised insects, and have apparently become 

 degenerate in consequence of the completeness of the 

 provision made for them by the intelligence or special 

 instincts of the parent. They are, as Brauer humorously 

 says, like the sluggards in Hans Sachs' Lubberland, 

 who required roast pigeons to fly into their mouths. I see 

 in them no mark of a primitive insect. 



Brauer in 1869 was ready to derive the maggot from 

 the caterpillar, and the caterpillar from the Campodea 

 (p. 310). He points out, very truly, that the reduction of 

 the larval head of the Diptera may be gradually traced 

 from forms in which it is perfectly developed. It is a pity 

 that he did not bear his own explanation in mind when at 

 a later date he attempted to arrange the Diptera 

 Nemocera by characters largely drawn from the degree 

 of development of the larval head. The unsatisfactory 

 nature of the result has been pointed out by Baron Osten 

 Sacken {Berl. Ent. Zcits., Bd. xxxvii. p. 417, 1892). 



That Brauer's arrangement of the Nemocera does not, 

 in the opinion of experts, associate allied forms, shows 

 that he has been unfortunate in his use of larval 

 characters. Could that result have been anticipated ? Is 

 there any general objection to the employment of lar\'al 

 characters in the definition of large groups of insects ? 

 I think that there is. In his paper of 1869 Brauer, 

 following Fritz Midler, remarks that the development of 

 various insects has been either abbreviated or falsified. 

 He thinks that the Hemiptera have lost a transformation 

 which they once possessed. He thinks that Dipterous 



NO. 1364, VOL. 53] 



larvae and others have been acted upon by conditions of 

 life which have not affected the imago. Yet he has 

 employed characters which he knew to be highly adaptive 

 and also finely gradated, for the definition of his tribes 

 and families. Brauer is both a systematist and a philo- 

 sopher, but his system forgets his philosophy. 



Primitive insects, we may suppose, attained the 

 Campodea form in the &gg, after which they merely 

 increased in size without important modification of 

 structure. The next step opened the way to extraordinary 

 developments, which were not, however, immediate or 

 necessary consequences. Certain insects acquired wings 

 as adults, while others remained wingless and pursued 

 the old life. The acquisition of wings did not as a 

 matter of course greatly affect the habits of the species. 

 Some, like the grasshoppers, crickets, and cockroaches 

 of to-day, continued to run about on their long legs in- 

 all stages, and divided their food with the same kind of 

 jaws as their wingless progenitors. But when full 

 advantage was taken of the new means of locomotion,, 

 the life-history was profoundly affected, the two extremes, 

 early and late, being acted upon in opposite ways. The 

 imago grew more active and quicker to discover the best 

 sites for egg-laying, gradually undertaking the whole 

 function of dispersal of the species. The larva, thus- 

 relieved from choice and travel, became slow and clumsy, . 

 escaping its enemies by protective resemblance or 

 burrowing. It came to be more and more exclusively 

 occupied with feeding, while the adult, except where the 

 business of egg-laying was unusually protracted, fed less 

 and less, sometimes not at all. 



The quiescent pupal stage seems to me to have arisea 

 from the contrast between the degenerate, slow, voracious 

 larva and the active, highly organised and sensitive imago. 

 Sagacity and activity gradually declined in the larva, and 

 became exalted in the imago, until the extremes of the life- 

 history became so unlike that they could only be reconciled 

 by profound changes, incompatible with locomotion and 

 feeding. 



I quite agree with Lubbock's remark, "that the 

 apparent abruptness of the changes which insects 

 undergo, arises in great measure from the hardness of 

 their skin, which admits of no gradual alteration of form, 

 and which is itself necessary in order to afford sufficient 

 support to the muscles." The hardness of the skin in 

 insects and other Arthropods involves periodical moults 

 in order that the body may increase in size. Pupation is 

 an exaggeration of one of these moults, the subsequent 

 escape of the imago is an exaggeration of another. 

 These two moults are the last but one, and the last of all, 

 and the pupal stage, where there is one, intervenes 

 between them.^ An ordinary moult gives opportunity 

 for effecting slight changes in the chitinous cuticle. The 

 new skin is not necessarily moulded precisely upon the 

 old one. If increase of size is required, the new skin can. 

 be made a little larger, and accommodated within the old. 

 one by wrinkling or folding. It is in this way that the 

 wings of an Ephemera, a dragon-fly, or a male cock- 

 roach gradually attain their full size. If projections of 

 unusual length are to be formed beneath the old skin,, 

 they can easily be telescoped into the body ; a process 

 which attains a high degree of complexity in some 

 insects. 



Many insect transformations, too familiar to be detailed 

 here, illustrate the great facilities afforded by the change 

 of skin for replacement of organs lost by degeneration, or 

 for development of new ones, more elaborate than any 

 possessed by primitive insects. But for these facilities 

 I imagine that larval degeneration would never have 

 gone so far as it has done in insects ; the price to be 

 paid would have been too heavy. 



1 It has come to pas.s, by .some process which I caiinot trace, that in. 

 Ephemeridse, where there is no pupal stage, the fly quits the water at the- 

 Ixst moult but one, and immediately afterwards casts another very thin skin. 



