THE LIFE-HISTORY OF A LEPIDOPTEROUS INSECT. 193 



Between the early embryos of mammals, birds and reptiles there is such 

 a strong likeness, that Von Baer tells us that, of two embryos in his 

 collection which were unlabelled, he could not say even to what class 

 they belonged ; they might be lizards, birds or mammals, " so com- 

 plete is the similarity in the mode of formation of the head and trunk 

 in these animals." Again, many of the Crustacea are exceedingly alike 

 in their early stages, although they become very different in the adult 

 stage. When we come, however, to genera and species, we find that 

 the similarity of their early stages is much more pronounced, the 

 similarity extending even to small matters of detail. Thus the furze 

 which when mature bears prickly leaves, has in its early stages the 

 ordinary trifoliate leaves of its leguminous allies ; the young of the 

 lion is striped like so many other carnivora ; the young blackbirds are 

 spotted after the characteristic manner of the thrush family — and so on. 

 It must be noticed that these similarities in embryonic characters do 

 not usually bear any relation to the conditions of existence. Young 

 mammals, birds and reptiles, passing through their earlier stages under 

 such different conditions, alike have a peculiar development of the 

 branchial arteries. It cannot be supposed that, in the womb of the 

 mother or in the egg of a bird, these have any functional value or any 

 relation to their then mode of existence, and we can only look upon 

 the peculiarity as a survival of a common ancestral feature, which at 

 one point in the line of descent had a fundamental value. 



3. — On the effect of the differing conditions of EMBRYONIC 



LIFE. — I have already intimated that embryonic life cannot be held to be 

 limited to the egg-stage, and the proportion thereof that is completed 

 in that stage differs greatly in the different classes of the Animal 

 Kingdom. The embryonic changes in the egg of a bird bring the 

 young bird very much farther on towards the adult, both in form and 

 development, than those in the egg of an insect, in which the larval 

 and pupal condition are also distinctly embryonic. 



It will be readily understood that when an animal embryo completes 

 its development to a great extent within the body of its parent (animal), 

 or is entirely dependent on its parents for nourishment (bird), there is 

 less need for it to take on any special characters for its own protection 

 than when it becomes actively indejjendent early in life (crustaceans and 

 insects, &c.). When, too, the method of life, the habits, environment, 

 &c. of the active embryonic form are entirely different from those of 

 the adult, it is evident that the difference between them must be 

 correspondingly great if the adaptation of the two forms to their 

 different conditions of life is to be equally perfect. We may find, 

 therefore (and the Lepidoi)tera give us a number of instances) that the 

 larvas of allied species differ very greatly owing to the diffei-ence of 

 their habits, &c., whilst the imagines are very similar ; conversely the 

 larvae may show a close relationshijj, though tlie imagines may be very 

 different ; the larvfe and imagines Avith similar habits may both bear a 

 strong resemblance to each other. Thus the larva? and pupaj of Viminia 

 venosa and V. rumicis show throughout a very strong resemblance, 

 which rejiresents a real relationship, whilst their imagines are as 

 different as can well be supposed, indeed, until (piite recently, Viminia 

 venosa was, on the strength of its imaginal appearance, separated 

 generically from rumicis, and its superficial resemblance in the imago 

 state led to a general belief among entomologists that it was allied to 



