FROM EMBRYOLOGICAL DATA. 9 



Caterpillars as such have been mmutely described and figured. The differences 

 they show in form and color, and even in the details of their external appendages, 

 have been noticed in most species. The chrysalis, also, has generally been described 

 and figured, though perhaps not with the same degree of minuteness as the cater- 

 pillar, whilst nothing can exceed the minuteness and precision with which natural- 

 ists have described and figured the perfect insects. Indeed, the illustrative works 

 we now possess of this class exceed in beauty, perfection of execution, and mi- 

 nuteness of detail and coloring, all the illustrations of a similar kind relating to 

 other classes. But those periods of transition in the life of Lepidoptera, those short 

 intervals during which the caterpillar passes into the state of a pupa, and the pupa, 

 again, into the condition of the perfect winged butterfly, have been more neglected, 

 probably for the very obvious reason, that, during these periods, as is well known, 

 those animals are more delicate, and more apt to die or to be injured if disturbed. 



Perceiving, however, the imj)ortance of a close investigation of these stages in 

 their metamorphosis, Avith reference to a full understanding of the process by Avhich 

 a lively, ornamented worm passes into the condition of a mean, enfeebled, mummy- 

 like animal, inclosed in a hard case, deprived of external appendages of any kind, — 

 and then, again, of the process by which this passes into an insect provided with 

 well-articulated legs, a long proboscis, prominent antennae, and large wings 

 adorned with diversified colors, — I undertook to secure a sufficient number of larvae 

 of several species of Lepidoptera, to afford me ample opportunities for deliberately 

 investigating them during the period of their transformation. Some of the results 

 of these researches I shall now relate. 



In order not to be misunderstood, I would mention that I allude here to the 

 actual transition from one of the temporary stages in the metamorj)hosis of these 

 insects to another, that is to say, to the passage of the caterpillar to the chrysalis, 

 and that of the chrysalis to the perfect Lepidopter, and not to the different stages 

 under which these insects appear temporarily for a longer or shorter time, and 

 which are already so well known. Nor do I mean to introduce the subject of the 

 changes in the internal structure during those metamorphoses, which have been so 

 ably investigated by Herold. My chief object is to illustrate comparatively the 

 morphology of these different stages in their transitions into each other. 



As the most prominent and striking changes occur in the external form, my first 

 object was to investigate the structure of the skin, especially of its inner layers, 

 which seem to be the seat of a peculiar activity in this process of transformation. 

 But I must confess that, up to this day, I have been unable to ascertain how the 

 new skin developes under the old, at each moulting, in any of the insects. I can 

 only suggest that the fact of extensive blood-currents flowing over the lower part 

 of the body, and upwards along the lateral Avails of each ring, to meet again the 

 dorsal vessel, is very probably connected Avith this important function, and increased 

 activity of the skin. But hoAV the ncAV layers are deposited, hoAv the appendages 

 themseh'es, which are successively modifled, or entirely formed ancAv, are dcA^eloped, 

 and Avhat is the nature of the function by Avhich they are produced, I am unable to 

 state. The results at Avhich I have arrived do not go beyond an illustration of the 



VOL. II. ART. 6. — 2 



