INSECT. 



831 



pre-exist as germes, but are oitned successively from 

 the rete mucosum, which itself is formed anew upon 

 every change of skin ; these formations being attri- 

 butable to the action of a power which he terms 

 the vis formatrix. 



Against the latter theory, Messrs. Kirby and Spence 

 have raised various objections, none of which appear to 

 the author of this article to be of sufficient weight to 

 overthrow it in favour of the old theory of S wammerdam. 

 The first of these objections is, that Dr. Herold em- 

 ploys the high-sounding term, vis formalrix, to conceal 

 his own ignorance of causes, when endeavouring to 

 penetrate within the sanctum sanctorum, which is 

 not permitted to vain man to enter a plan adopted 

 in all ages, and instanced in the adoption of such 

 words as Plastic Nature, Epigenesis, Panspermia, Idea 

 seminalis, Nisus formativus, &c. It is evident from 

 these observations, that these authors would endea- 

 vour to fix upon Dr. Herold a charge of infidelity, 

 in supposing that the structure of an insect possessed 

 of itself a power to mould itself according to its 

 own formative will and power. And this is evident, 

 because in a subsequent page they adduce the fact, 

 with which every physiologist is acquainted, that 

 the developments and acquisition of new parts and 

 organs, by insects undergoing metamorphoses, have 

 taken place according to a law, which regulates their 

 numbers, kinds, and times, since the first creation. 

 But surely they are not authorised by Dr. Herold's 

 views and statements, in wielding against him this 

 powerful (if maintainable) argument, since it must 

 be evident, that by the term vis jbrmatrie, Dr. 

 Herold meant not to imply any power independent 

 of the Creator, but simply thaymnciple of develop- 

 ment which, under the guidance of an Almighty 

 hand, is constantly in operation, not only in in- 

 sects, but in every other branch of the creation *. 

 It would be as unjust to assert, if a man, whose fin- 

 ger had just healed from a wound, and who should 

 thereupon say that he had gained a fresh layer of 

 skin by the action of his flesh, that he was an atheist. 

 But in the next place, Messrs. Kirby and Spence 

 do not deny the facts stated by Dr. Herold, that the 

 organs of the butterfly are not discernible in the 

 larva, but gradually become visible, as the caterpil- 

 lar throws off its successive coverings. They assert, 

 indeed, that, they can easily comprehend that pre- 

 existent germes, by the constant secretion of new 

 matter, in a proper state, may be gradually deve- 

 loped ; but find it impossible to conceive how, by 

 the action of second causes, without the intervention 

 of the first cause, the butterfly should be formed in the 

 caterpillar, unless it pre-exists there as a germe or 

 foetus. The question is not, however, whether the 

 butterfly be or be not inclosed as a fetus within the 

 caterpillar ; but whether, as Swammerdam evidently 

 intended, the various skins of the caterpillar, &c. 

 existed as distinct and visible germes within the 

 newly-hatched caterpillar; and this Messrs. Kirby 

 and Spence endeavour to support, by the argument 

 which they adduce from Bonnet, that " organs that 

 have no existence as to us, exist as they respect the 

 embryo, and perform their essential functions ; the 

 term of their becoming visible, is that which has 



* It is rather remarkable, that Messrs. Kirby and Spence, 

 after having thus endeavoured to brand Dr. Herold as an athe- 

 ist, should have expressed a supposition, that the skins of ser- 

 pents are formed under the old skin, from the rete mucosum, 

 (Vol. III. p. )Q1.) The cis formatrix of Dr. Herold, is of no 

 higher rank than the power implied in this expression. 



been, erroneously mistaken for the period of their 

 existence." 



The question, therefore, now assumes a new form. 

 It is not, as between Swammerdam (contending that 

 the successive skins of the caterpillar exist as distinct 

 and visible germes in the newly born caterpillar,) and 

 Dr. Herold (asserting that these skins are suc- 

 cessively produced from the rete mucosum), but 

 simply whether we are to consider with Kirby and 

 Spence, that these germes are pre-existent, though not 

 perceivable even by the application of the most power- 

 ful microscope, but which subsequently, " by the con- 

 stant accretion of new matter in a proper state, are 

 gradually developed ;" or with Dr. Herold, that they 

 do not pre-exist as germes, but are successively form- 

 ed from the rete mucosum. Having, however, di- 

 vested the arguments of the latter from the charge of 

 atheism which has been attempted to be forced upon 

 them, we really are not prepared to consider that 

 there are no grounds for the adoption of the latter in 

 preference to the former. It is true that Dr. Herold 

 discovered the organs of sex in the newly excluded 

 larva ; but these and other organs of the perfect but- 

 terfly, are those which, from their very nature, must 

 be regarded as requiring the greatest and most 

 gradual degrees of development ; but the case is 

 quite different with such temporary organs as the 

 skins of the caterpillar : but let us look to facts, 

 Messrs. Kirby and Spence are unable to adduce any 

 in support of the existence of invisible germes, but ac- 

 cording to Dr. Herold, there is not the least trace in 

 the young larva of the new skin, but this first origi- 

 nates towards the end of the first period of the cater- 

 pillar's life, a few days only before the old one is 

 stripped off. It is then observed that the mucous 

 and muscular layers of the skin separate all round, 

 from the epidermis, and then clothe themselves upon 

 the superior surface with a new epidermis. The de- 

 velopment of this new external skin occupies two or 

 three days, during which the caterpillar appears 

 sickly, and takes but little nourishment ; the old skin 

 then splits longitudinally along the back, and the 

 caterpillar emancipates itself from its old envelope by 

 drawing out the body. The epidermis, all the exter- 

 nal visible organs, and even the mandibles and palpi, 

 remain attached to the old skin. This moulting is 

 repeated several times. 



Various physiologists, and especially Dr. Vircy, 

 have endeavoured to trace an analogy between the 

 transformations of insects and the development of 

 some of the higher animals ; attributing, as Mr. Mac 

 Leay observes in his Horse Entomologies, the meta- 

 morphoses of insects to the shedding of an envelope 

 analogous to that which contains the fetus of the 

 more perfect vertebrata. And as every embryo, whe- 

 ther animal or vegetable, is inclosed in a tunic more 

 or less solid (its chorion), so proceeding with the 

 analogy, they conceive there must be some condition 

 for every animal, similar to the state of the foetus of 

 the more perfect animals, when surrounded by the 

 amnios of this state, and which in the hexapod insects, 

 they hold to be the larva, according to which the true 

 birth of the animal will be its exclusion from the pupa 

 case. This argument seems to have been derived 

 from an observation of Reaumur namely, that the 

 larva of insects ought to be regarded as an egg of an 

 extraordinary kind, endowed with organs of locomo- 

 tion and nutrition ; and that this analogy is also re- 

 tained during the period of the insect's existence in 



