TRANSFORMATIONS OF IMPERFECT FVPM. 79 



types, although we find none of those which are so 

 common among the diurnal butterflies. Such are the 

 leading variations or the most remarkable differences at 

 present known among the inactive pupae of the typical 

 order of annulose animals. But there is another modi- 

 fication which must here be noticed, because it comes 

 under our definition of a perfect chrysalis : this is called 

 coarctate; and is when the larva changes into a pupa 

 so entirely covered with a thick crustaceous shell, as to 

 assume the appearance of an oval egg, the surface of 

 which is smooth and glossy, without, in most in- 

 stances, exhibiting more than a slight indication of those 

 joints, segments, or angles, which are seen in all tlie 

 types before-mentioned. This sort of pupa is chiefly, 

 if not exclusively, found in the order of Diptera, or of 

 two-winged insects, and in that of the Hymemptera, 

 which includes the bees and wasps. MM. Kirby and 

 Spence consider this as a " fifth kind of pupae, which 

 are not, as in other instances, excluded from the skin of 

 the larvae, but remain concealed under it, and were hence 

 called by Linnaeus coarctate pupce : they may be termed, 

 in common language, cased nymphs. The envelope of 

 these is formed of the skin of the larva considerably 

 altered in form and texture." * 



(69.) Of imperfect pupae, or such as are active, and 

 resemble either the larva or the adult insect, there are 

 various kinds. The name given by Linnasus to these 

 semi-transformations, appears to us particularly objec- 

 tionable : he called them complete, — thereby leading us to 

 the erroneous supposition that they are the most com- 

 plete or perfect examples of the pupa transformation ; 

 the fact being, that they are, in this respect, precisely 

 the contrary : they not only greatly resemble the mature 

 insect in form, but are equally capable of eating and 

 moving. As these insects, however, cast their skins at 

 stated periods, and undergo changes, though slight, in 

 their external and internal conformation, they are justly 

 regarded by all authors as undergoing metamorphosis, 

 * Int. to Eiit. i. 69. 



