THE ENCASEMENT THEORY 641 



stage there is an atrophy of the antennae and legs. On the other 

 hand, at this stage the female completes its metamorphosis. 



The rudiments of the wings arise on the edge of the dorsal and 

 ventral side of the 2d thoracic segment, and this, we would remark, 

 is significant as showing a mode of origin of the wings intermediate 

 between that of the manometamorphic and holometamorphic insects. 

 (See pp. 137-142.) While Schmidt could not ascertain the exact 

 structure of the imaginal buds, he says " in general the process of 

 formation of the extremities is exactly as Weismann has described 

 in Corethra.'' The two later pupal stages are "as in other metabolic 

 insects." (See p. 690, Fig. 637.) 



Thus far the internal changes in the metamorphosis of the 

 Coleoptera have not been thoroughly studied. They are less com- 

 plete than in the other holometabolous insects, the differences be- 

 tween the larva and imago being much less marked than in the 

 more specialized orders, and so far as known all the larval organs 

 pass, though not without some great changes, directly into the 

 imaginal ones, the only apparent exception being the mid-intestine, 

 which, as stated by Kowalevsky, undergoes a complete transforma- 

 tion during metamorphosis. The following account, then, refers 

 almost wholly to the Lepidoptera, Hymenoptera, and Diptera. 



a. The Lepidoptera 



The first observations on the complete metamorphosis of insects 

 which were in any way exact were those of Malpighi, in 1667, and 

 of S \vammerdam, in 1733. While the observations of Swammerdam, 

 as far as they extended, were correct, his conclusions were extraor- 

 dinary. They were, however, accepted by Reaumur and by Bonnet, 

 and generally held until the time of Herold in 1815, and lingered 

 on for some years after. The rather famous theory of incasement 

 ("emboltement") propounded by Swammerdam was that the form of 

 the larva, pupa, and imago preexisted in the egg, and even in the 

 ovary ; and that the insects in these stages were distinct animals, 

 contained one inside the other, like a nest of boxes, or a series of 

 envelopes one within the other, or, to use his own words: "Animal 

 in atiiiitali, m'n pajtilio infra eracam reconditus." 



This theory Swammerdam extended to the whole animal kingdom. 

 It was based on the fact that by throwing the caterpillar, when 

 about to pupate, in boiling water, and then stripping off the skin, 

 the immature form of the butterfly with its appendages was dis- 

 closed. Malpighi had previously observed the same fact in the 

 2 T 



