INSECTA. 



869 



be seen that a large majority of insects have four 

 if existence, the egg, the larva, the 

 |>ii|i;i, and the imago or perfect state. I 'mil 

 very lately, it was supposed that this peculiarity 

 <>t existing at different periods under such 

 dillrrent forms lirlonged only to this class of 

 the Invertebrata, but recent observation,* as 

 shown in the article CHIRIIOPODA, \c.,f lias 

 made it appear that there are other d 

 also which undergo metamorphoses, although 

 in no instances do the animals continue so long 

 in their preparatory states, nor undergo such 

 remarkable changes of form in passing from 

 one state to another, as insects. 



Tin- egg. In the egg, or earliest stage of 

 extra-uterine existence, the insect continues for 

 a longer or shorter time according to external 

 circumstances. We have at present only to 

 notice the external form, markings, and colour 

 of the egg, which vary as greatly in the dif- 

 ferent species as the locality in which it is 

 placed by the parent The greatest variety of 

 these occurs among the Lepidopterous insects. 

 In some, as in the butterfly, Pontin braaica, 

 the egg is of an obtuse conical figure, like a 

 Florence flask, and is beautifully ribbed and 

 beaded on its exterior surface ; in others, as in 

 one of the night-moths, Acronycta Psi, it is 

 ribbed, and is flattened like a lens;J in the 

 small but beautiful butterfly, Thecta betultr, 

 it is shaped like a turban ; in CtuiocawjMi 

 ncustria, which glues its eggs together like a 

 ring around the small branches of fruit-trees, 

 it is cylindrical, and flattened at both ends, 

 aud in the puss-moth, Centra v'mula, its form 

 is compressed and lenticular. Among the Neu- 

 roptera, llemiptera, and Diptera there are other 

 limns equally curious. The lace-winged fly, 

 ClirysojM perla, suspends its egg in the air upon 

 a long pedicle ; || the egg of the water-scorpion, 

 Nepa cinerea (Jig. 352), is encircled at one 

 extremity by a coronet of rays or processes.H 

 while in one of the dung-flies the egg has two 

 projecting appendages which have somewhat 

 tlic appearance of ears. The color and mark- 

 ings of the egg are not so various as its form. 

 In the common green grasshopper, Acrida 

 ririilissiiiiit, it is ureeii, like the seeds of some 

 plants. In t'i'tiiciii riciifit and Tipulii iileracca 

 it is perfectly black, and in other instances, as 

 in OtluiH'stis potnluria, it is beautifully en- 

 circled with bands of white and green, or is 

 speckled with darker spots, like tin 

 of birds, as in LnMMMpd ijiifrcim. The 

 prevailing colours, however, are yellow, as in 

 the 1 cylindrical eggs of the oil-beetles, the .1/r/nc 

 and ZVommtn; or white as in the tlesh-flies, 

 Miisfn ri'iiiittiriu and di>mistica ; or perfectly 

 translucent, as in the saw-fly of the turnip, 

 Al/iiilin ciiilitoliic. The external markings 

 and sculpture on the egg are not less remark- 

 able than its general form and colour. Some- 



1'hil. Trans, part ii, 1835. 



t Vol. i. p. 692. 



i Sepp. 



5 lii. quoted by Hurmcisior, Manual of Ento- 



nmlnuy ( Trans, t. p. li:i:). 



1| Reaumur, Kirliy and Spenco, vol. iii. p. Wj. 

 II SwumiiKrilitiii liib. Nat. t. iii. tigs. 7 and 8. 



times the egg, as above stated, is ribbed and 

 leaded, s( ..... 'times excavated over its whole 

 surface into regular cells like a honey-comb, 

 at others it is imbricated like the tiling of a 

 house, but in the greater number of instances 

 it is smooth as in other animals. 



These peculiarities of form and color appear 

 in many instances to have relation to the cir- 

 cumstances under which the egg is deposited 

 by the parent, to its preservation, or to the 

 locality in which it is placed. The e^g of 

 Scntopfiaga stercoraria, KIRBY, is only par- 

 tially inserted into recent cow-dung,* with its 

 auricular processes, through which it is sup- 

 posed to respire, exposed to the influence of light 

 and air ; that of Chrysopa perla, K., the lace- 

 winged fly, is attached by its pedicle in the 

 midst of crowds of Aphides, upon which the 

 young larva is to subsist ;f while the core- 

 netted eggs of Nepa (Jig. 352) are inserted into 

 the stems of water-plants, with their processes 

 only exposed,J probably for the purposes of 

 respiration, until the enclosed germs are stimu- 

 lated into active existence by the vivifying 

 influence of light and air, without which 

 perhaps they would perish. This indeed 

 happens with the eggs of the great water- 

 beetle, Hydruus piceut (Jig. 330) which, ac- 

 cording to Lyonet, are deposited in a little nest 

 that floats upon the surface, and from which 

 the larva; escape into the water immediately 

 they are developed. We have found that if 

 the eggs of this insect be allowed to fall to the 

 bottom of a vessel of water, and remain there 

 for some days, organisation proceeds in them 

 for a day or two, after which they perish. For 

 a similar purpose the eggs of Alhuliii ccnti- 

 J'olite (fig. 355), which require a high atmos- 

 pheric temperature for their speedy development, 

 are inserted into little spaces between the cuticle 

 and purenchymatous tissue of the leaf of the 

 turnip. In each of these instances the object 

 to be insured is the safety of the egg itself; 

 either its preservation from external injury, or 

 its full exposure to atmospheric influence to 

 accelerate its development. It may be re- 

 marked as a general rule, that those eggs from 

 which the larva; are most rapidly developed 

 are those which require the highest tempera- 

 ture and fullest exposure to the atmosphere. 

 These are the external circumstances which 

 greatly influence the development of the germ 

 into the state of larva. 



7V IdrvH. Immediately the insect is liber- 

 ated from the external coverings of the egg it is 

 called a larva. It is so designated from its 

 then being as it were under a mask or in dis- 

 guise, and unable to fulfil one of the principal 

 "l)ji i ts of its existence, the continuation of its 

 kind. In some species, as among the Aptera, 

 it has at this period the form of the parent, 

 from which it differs in nothing externally but 

 size, beui'.: always very much smaller. Instances 

 of this kind occur in the Pediculi and AiVini 

 ;.">1). In other species, examples of 

 which are seen in the Cimici's, lilatlte (fig. 343), 



* Kirhy and Spencc, vol. iii. p. 97. 



t Reaumur, torn. iv. p. 376. 



; Kiitiy and Spencc, vol. iii. p. 95. 



