Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/669

 T R A

quired its brown colour. This however is not at all the eafe, for it can now walk as before, and thrufting out its head and the rings it had drawn in, can again acquire its former figure, which however it lofes afterwards at once, and be- comes rigid in a few minutes, and in two or three hours the (kin it has quitted, and which is now a fhell, becomes reddifh, and after a little more time acquires its proper chefnut colour. Ibid. p. 290.

This coat is now no more a fkin, but a fliell, and fit to per- form all the offices of one ; it is no longer connected to the body of the animal, but is become hard, brittle, and rigid. It may however yet be diftinguifhed, efpecialiy by the help ofr the microfcope, to be made up of a great number of rings, which may be more diftinctly counted than they could be in the worm : there are nine of thefe between the caps, which make the two ends ; two rings at leaft, without counting the head, go to the forming the anterior cap, which is purfed or wrinkled up like the top of a bag when clofely drawn to- gether ; but thefe folds or wrinkles do not abfolutcly meet and dole up the end. The microfcope Ihews at each extremity Of one of the diameters of this cap two little bodies not at all diftinguifhablc by the naked eye ; each of thefe is one of the anterior Itigmata.

On the two rings which follow this cap immediately, under- neath each of thefe itigmata ; there may be obferved a fmall band, very little elevated above the furface of the reft of the fhell. Thefe feem the two ftrongeft parts of the fhell, but they are in reality on the contrary the two weakeft, and are the places where the fhell is to fplit and open to give paflage to the fly. Ibid. p. 293.

On the cap which makes the other extremity of the fliell may be feen, the two pofterior ftigmata, thefe are the mod con fiderable in the creature, and are each a collection of three oblong ftigmata. Ibid. p. 294..

The Tram far motion in this fhell is double, before the infect becomes what it is to be finally, a fly like its parent ; the firft Transformation is into an oblong mats of matter, void of all form, either of the worm it was, or of the fly it is to be; but from this it by degrees affumes the figure of the nymph, in which all the lineaments of the future fly are diftin- guifhable. This Transformation (which is in thefe, and per- haps in all the worms that make a cafe of their own fkin, prior to their change into the nymph ftate) maybe called the change into the long ball or fpheroide, or into the ellipfoide. This fly-worm of the blue fly is one of thofe, which with moil difficulty Ihews this Transformation ; but on boiling it at a pro- per time and afterwards carefully opening the fhell, it will always be found in this ftate. Ibid. p. 295,296. It is a very eafy thing to be provided with thefe worms in their fliell ftate, in a fufficicnt quantity; and it is a very pleating examination to boil and open feveral of them daily, to fee the progrefs in their refpective Transformations ; by this means alter two or three days one may diftinguifh the legs on the anterior part of the body, but very mort ; the day following, the wings will begin to fhew themfelves, and the ends of the legs will be found extended toward the hinder part ; a day afterwards the end of the trunk may be diftin- guifhed, and the head begins to fhew itfelf. And finally the legs wdl be (ecn in their due length and proportion, and the reticular eyes will very plainly fhew themfelves. Ibid. p. 299. Several accidents, as the heat or cold, and drynefs and wetnefs of the feafon, contribute much to the forwarding or backward- ing thefe fucccfllve changes: in fummerthe worms will remain fomctimes in a moift earth fix or feven days without chang- ing ; and others will acquire their fhell-ftate in a dry earth in two or three days : a moift earth may alfo very eafily much impede the fecond Transformation, from the ftate of the ob- long ball into the nymph. Since in order to this there is re- quired an evaporation of a great deal of moift lire, which is in the fhell ; and this cannot be fuppofed to be fo readily per- formed in a moift as in a dry place; and that fuch an evapo- ration is required is very plain, from the change of weight in the fhell in thefe two ftates; for when the contained ani- mal is in the form of its oblong ball, the fhell is in the whole heavy enough to fink in water ; but when it has acquired the form of the nymph, it is io light that it fwims. Ibid. p. 305. The time required for thefe feveral changes often differs a little, and Ibmetimes confiderably ; but at a medium it ftands thus : the worms which have been feen to creep into the earth on the 2 i ft of April, have come out perfect: flies on the 16th of May, and that in a cold feafon for the time of the year. The fhells of feveral of this brood opened on the 28th and 29th of April, {hewed the iafeft in form of the oblong ball ; the parts of the nymph were not difcoverable in any opened be- fore the 30th of April ; but thefe fhewed the legs of a third part of the length of the body : thefe nymphs had all a cavity on their anterior part j but thofe opened on the 2d and 3dof May had not this cavity; but the dart and hooks vifible in it before were now applied againft the furface of the cap, and the head of the future fly fhewed itfelf: on the fourth of May the trunk appeared very fair, and the reticular eyes were be- come vifiblc, tho' all that was now vifible, was incn thro' a thin and delicate fkin. Ibid. p. 306. On the 6th of May the antenna were diftingu'dhable, and their Vol. II. Suppl.

T R A

form very perfectly finifiied ; on the 7th the fmooth fmallet eyes were diftingmfhable. The 8th of May the reticular eyes had acquired a reddifh colour ; the 9th the colour was vet more natural ; the 10th thefe were become of a deep red, and the fmooth eyes looked reddifh ; and on fome of the ftigmata of the nymph, the fpots of the former worm were now eafily difcoverable ; on the nth the nymphs were all become hairy; on the 1 2th thefe hairs were more vifiblc, and of their natural colour, and the legs were become greyifh, and of their full length. The lips of the trunk were of their natural colour, almoifc black ; and the antennae began to be coloured ; and the whole fliape of the fly was very diftinct. The 13th, 14th, and 15th days made no great changes, as the parts were now already formed, and only wanted their proper ftrength and confiffence ; and on the Lift day, before their egrefs, and not before, did they appear to have any power of motion ; which, as foon as they had it, was applied to the freeing themfelves from their (hell, and coming out in the form of the parent fly. Ibid. p. 308.

The changes a multitude of other fly-worms undergo, and their {hells made of their proper fkin, are the fame in all el- fentbl points with thofe of the flics firft mentioned. Soms fpecies have their fliell more deeply annular, others almoft entirely fmooth ; fome have the two ends Ibmewhat pointed, and others only one of them fo ; and in fome this larger in- flated end is the anterior, and in others the pofterior. Ibid, p. 309.

Swammerdam, to whom the world is indebted for the fitft true infight into the wonders of the infect, world, has evidently proved, that what had before been called by the pompous and myfterious names of changes and Transforma- tions of one animal into another, as of a worm into a fly, and the like, is, in reality, no more than a gradual and natural growth and evolution of the parts, not any metamorphofis of them ; and this growth rcfembles very well, when judicioufly confidered, not only the increafe of other animals, but alio the natural budding and increafe of plants. The progrefs of thefe changes, as they are called, in infects, is exprefled by two different terms in their two moft remark- able ftates ; the words are the njmphm and the chryfalis. Thefe words are often mifunderftood, and even mifapplied and confounded by authors one with another. What the moft accurate authors have originally meant by them, how- ever, is this :

The nympha is the change of the worm, which carries the proper fhapc of the future little animal ; and the chryliilis, or aurclia (for thefe words have the fame fenfe, derivation and meaning) the change of that caterpillar, which fhews no parts at all of the animal that is to come.

This is the regular meaning of the two words; but Swam- merdam proves them to exprefs, as the fchoolmen call it, diftinction without difference, for that he was always able to difcover the feveral parts of the future animal, as well in the chryfalis as in the nympha; and that others had only made the difference from the want of due attention and appli- cation.

This author therefore makes no other difference between the nympha and chryfalis, but this ; that fince the parts of the future animal are not fo plainly difcernable in the chryfalis as in the nympha, and a fine golden colour is very common in the more obfeure ftate of the animal, and is not found on any of thofe fo perfect, as to be vulgarly called nymph ; it may be proper to exprefs, by certain forms of fpeech, thofe flight but obvious differences ; but not to give them the pompous names of Transformations, and the like. The nymphs he therefore calls fimply puppets, and the chryfalis's by the name of gilt puppets.

Swammerdam refers the general changes, as they are called, of the infect tribe, into four clafles, one or other of which takes in that of every known infect, a very few excepted, whole progreflions have not yet been fufliciently inquired into, to afecrtain their nature. The fpur general clafles, or ranks of changes, are diftinguifhed by four different ways of production, change, and growth.

The firft rank, which he cxprefles by the name of nymph- animal, hath a little animal fully formed in the egg, which, after the evaporation of the fuperfluous moifture, comes forth perfect, and fo grows up. Such is the loufe, and the like. The fecond clafs are diftinguifhed by the name of nympba-ver- mtculus. Thefe have the parts of the future infect imperfectly fliaped in the egg, and, after hatching, leave the creature to acquire its perfection vifibly by outward food. Of this kind are the grafshopper, the locuft, the cricket, and many other the like creatures.

The third clafs he diftinguifties by the name of the nympha- chryfalh, or nympha-aurelia, Thefe, after hatching, obtain their perfection darkly, and not till after the cafting off the laft (kin; fuch are the butterfly and the like. The fecond and third clafs agree in this, that not a perfect animal, but a worm is produced from the egg, and precedes the growing of the perfect parts ; yet with this difference, that in the fecond the little creature grows up manifeftly and obvioufly to the eye ; hut in the third all is in dsrknefs and obfeurity under the (kin, and, as it were, within the body of the creature.

S s s s The