INSECT. 



843 



full size, and the abdomen is not yet reduced to 

 the size which it will possess in the imago state. 



Fig. 48. Disengaged pupa of Stratiomys chamseleon. 



Pupae are ordinarily of an elongated oval form, 

 the thickest part being towards the head ; the body 

 is generally smooth, but in some instances various 

 spines or hairs are to be observed upon various parts 

 of the body ; and others, especially the chrysalides 

 of butterflies, are angulated, as described in our 

 article CHRYSALIS. In some aquatic pupae, as 

 described in our article CHIRONOMUS and CULICID^E, 

 the back of the front part of the thorax is furnished 

 with exserted breathing organs. The structure of the 

 terminal segment of the buoy is also variable ; one of 

 the most remarkable variations, essentially serviceable 

 in effecting the suspension of suspended chrysalides 

 has been described in our article BUTTERFLY ; and 

 it may here be noticed that in those species of 

 Hymenaptera, which have the ovipositor long arid 

 exserted, it is generally curved upon the back of the 

 abdomen, although in some it is stretched out at 



Fig. 49. Pupa of an Ichneumon and Callimome 



length. In many of the woodrlvoring species of 

 Lejjidoptera, ( as, for instance, the Goatmoth ) the 

 abdominal segments of the pupa are furnished with 

 transverse ridges of minute hooks, which are service- 

 able to the insect, when about to assume the imago 

 state, in working its way to the orifice of its burrow, 

 the hooks, by the alternate contraction of the 

 abdominal rings, being employed as anchors in 

 preventing the insect from falling backwards. 



Fig. 50. Lateral view of the pupa of the goat-moth, lettered 

 as Nos. 46, 47, and 48 : and T 1, T 2. and T 3,- being the three 

 thoracic segments ; XX, two of the rows of hooks. 



There is a curious circumstance connected with 

 the development of the insect structure, especially 

 interesting as regards the pupa state of insects, 

 and it is one which has hitherto received but very 

 little attention. In the larva state the body is 

 composed of the ordinary and typical number of 



segments, but in tne perfect state some of the seg- 

 ments are not to be found. The change, therefore, 

 must take place at the period ol the insect's assum- 

 ing the pupa state. Dr. Ratzeburg, indeed, 

 accounted for the loss of one of these segments, by 

 asserting that the head of the pup^a of the bee 

 corresponds with the head and first segment ot 

 the body of the larva ; but this, as we have already 

 said, is certainly inaccurate, as we hare proved by 

 direct observation, and as is further evidenced by 

 the leg-bearing structure of the first segment in 

 many larvae. The loss must therefore occur in the 

 abdominal segments ; but upon this branch of the 

 subject we require more direct investigations than 

 have yet been devoted to its elucidation. As re- 

 gards the segmental development of the earwig, 

 an elaborate paper has lately been read before the 

 Entomological Society, but it is not yet published. 



Pupae, in general, are of a dirty white colour 

 when their situation is under ground, or in cases 

 artificially constructed by the larvae. Those, more 

 especially which lie naked under ground, are of 

 a dark bright brown, whilst those which are naked, 

 and exposed to the action of the light, are more 

 variable in their tints, some being gilded as in the 

 aurelise or chrysalides of butterflies. 



The period passed by insects in the pupa state is 

 very variable, the variations extending from a few days 

 to as many years. Ordinarily, its extent is determined 

 by the circumstances to which we have alluded in our 

 observations upon the duration of the larva state; 

 that it is chiefly dependent upon the temperature 

 of the atmosphere. Providence has wisely ordained 

 that the development of the perfect insect shall not 

 take plaoe until the season when proper food for its 

 own sustenance is at hand, or a proper situation for 

 the deposition of its eggs is to be discovered. Hence 

 some insects are produced earlier, and others later, 

 in the season ; and in doubled brooded species, or 

 those of which there are two generations in a year 

 the early brood passes but a very short time in the 

 pupa state, whilst the later brood remains throughout 

 the winter as pupa?. Hence Reaumur was enabled 

 by experiments with chrysalides to abridge or extend 

 their lethargic state by the artificial heat or cold ; the 

 chrysalides of various lepidopterous insects, which 

 would not ordinarily be produced until spring, being 

 placed in a hot-house, and the butterflies being deve- 

 loped in the middle of the winter, the contrary effects 

 being produced when they were placed in an ice- 

 house. Hence it is evident that by the action of aii 

 increased temperature a certain evaporation of the 

 fluid matter, with which the newly-formed chrysalis 

 is filled, takes place ; but we can by no means agree 

 with Kirby and Spence, that " this necessary trans- 

 piration, other circumstances being alike, must take 

 place sooner in a small than in a large pupa ;" and, 

 consequently, " that small pupa3 continue in that 

 state a shorter time than those of larger size :" 

 indeed, we are disposed to question the correctness 

 of the latter assertion, and to say, on the other hand, 

 that the duration of the pupa state is totally indepen- 

 dent of size. We could adduce hundreds of ex- 

 amples in support of our assertion, but it will be 

 sufficient for our purpose to observe that the largest 

 lepidopterous insect, the great Death's-head moth, 

 requires, according to Harvarth, but one month at 

 the end of autumn, when the weather has been 

 comparatively cold, to undergo its pupa state. If 



