110 NATLKAL IIISTOUY. 



race. Generally the sinaller species terminate it much sooner tlian the 

 larger, hut there are many exceptions to this. This has been explained 

 by the transpiration which is necessary before a chrysalid can arrive at 

 maturity, and by the evaporation of the fluids, which is performed much 

 sooner in the small than in the large chrysalids. This has been proved 

 to be a fact by Keaumer, who retarded the exclusion of the insect by 

 keeping the chrysalis in ice, and hastened it by the application of heat. 

 But we do not yet know why, of the same brood, under the same cir- 

 cumstances, so far as appears, some chrysalids go through their changes 

 much more speedily than others. 



The mode in which caterpillars change into chrysalids also varies 

 according to the race. Some, as that commonly called the siU:-u-nrm, 

 spin cocoons to envelope the chrysalid, whilst others, as the great mass 

 of the Rhopalocerata, are entirely naked. The latter have three differ- 

 ent modes oi' performing their metamorphosis, and it is upon these that 

 our nomenclature is partly based. In some, which we call succincii^ (suc- 

 cinct,) the chrysalis is fastened by the tail end and by a transverse band 

 in the form of a girdle, at every variety of inclination ; such are the Paj^- 

 iflo, Pieris^ Sec. In others, which we call suspense (suspense,) it is pen- 

 dant and only fastened by the tail, as in the Vanessa^ Satyrtis, &c. In 

 the third class, which we term involuti, (involute) it is rolled up in leaves 

 or in a thin web, protected externally by a number of transverse threads. 



The Heterocerata have two principal modes of passing into the chrys- 

 alis state ; some penetrate into the earth, others fabricate their cocoons 

 upon its surface. There is nothing more wonderful or more varied than 

 the instinct, we might say the intelligence, which these caterpillars dis- 

 play in securing and defending themselves against their enemies. The 

 cocoon of the silk-worm is undoubtedly one of the most interesting in 

 respect to its use to us. but others are fabricated in a much more remark- 

 able form. 



When the period of its exclu.sion, or as it might be termed, resurrec- 

 tion, has arrived, the chrysalis changes its color, becomes soft and trans- 

 parent, and sometimes shows through the cases of the wings the design 

 and colors of the butterfly. The efforts of the prisoner split it longitu- 

 dinally at the thorax ; the opening is speedily enlarged and it comes forth 

 with perfect ease. But when tlie chrysalis is confined in a hard and co- 

 riaceous cocoon, as that of certain Bomhyces^ Stc. or in a cocoon of pure 

 silk, the gates of another prison must be opened. For this operation the 

 means vary with the race. In some the instinct of the caterpillar has 

 foreseen these obstacles, and everything is found arranged in a most 

 wonderfifl manner for l!ic moment of the metamorphosis; for example. 



