78 NATURAL ARRANGEMENT OF INSECTS. 



deeper and deeper^ until we have the Sphinx Atropos as 

 the type and perfection of subterranean pupse. The 

 greatest part of the night-moths (^N^octuides) possess 

 this metamorphosis, which may also be found in the 

 aberrant examples of the other tribes of moths ; but in 

 the two first mentioned, the Sphingides and the Noc- 

 tuides, it is most prevalent and typical. The most 

 complicated sort of pupa, however, is that into which 

 the silkworm tribe are changed ; for here we have a 

 surprising display of preparatory caution and indus- 

 trious skill. It seems hardly necessary to describe in 

 this place the pupa or cocoon of the common silk- 

 worm, or rather caterpillar, except to notice its general 

 structure. There is a provident care in the prepa- 

 rations made by all insects of this tribe, which is very 

 remarkable ; — they envelope themselves in an oval com- 

 pact ball of the most delicate threads of silk ; these are 

 drawn from their own bodies; and they contrive, in 

 some unexplained stage of the operation^ to affix the 

 whole, externally, to a firm object. Now, this is evi- 

 dently a very near approach to the same form of pupa 

 as that which is so slightly developed in the skipper 

 butterfly before alluded to; but the difference is this, — 

 that in the silk-spinning caterpillars, the web or cocoon 

 is so firm and compact as to resist the weather ; whereas, 

 in the other insect, the web is so thin that it can be 

 seen through, and consequently requires the additional 

 protection of a leaf or of some other substance. "VVe 

 may add, also, that in the former, the chrysalis is always 

 thick, cylindrical, and obtuse, particularly at the head; 

 while, in the latter, it always exhibits some appearance 

 of angles, and the head is more or less pointed. The 

 pupse of the true moths (Phalcenides) are mostly of 

 this latter description; that is, they spin a thin and often 

 almost transparent web, witliin the folds of a leaf, al- 

 though the form of the chrysalis itself is like that of 

 the silkworm. Thiis, in fact, is the typical form of 

 the pupje among the true moths; but in this tribe we 

 have representations of the terrestrial and several other 



