ON THE MIGRATION OF BIRDS. 11 



Our caterpillar,~after casting its skin and resting a little, begins again 

 to eat the leaves of the nettle. I may mention, that all caterpillars do 

 not cast their skins the same number of times ; but with respect to the 

 present ones, they cast their skins four times, and as they grow quickly, 

 the castings closely follow each other, at due intervals between. I 

 have traced this in two of these caterpillars, which were hatched from 

 eggs the 12th of July, in the following order. Their first casting of 

 the skins occurred on the 14th, the second on the 17th, the third on the 

 21st, and the fourth on the 26th. They then continued to eat and 

 grow till the 15th of August, when, having completed their growth, 

 and reached their full age as caterpillars, they left off eating, and pre- 

 pared for entering upon their second stage of life, namely, that of 

 chrysalis, which has no resemblance to the caterpillar. This change 

 took place on the 17th of August. 



It hence appears, that the first stage of life, or the caterpillar state 

 of this insect, only lasts for five complete weeks ; but I must remark, 

 that in rearing the caterpillars for the purpose of observing their 

 changes, they must have fresh food every day, and in a warm day 

 twice, otherwise they will not thrive. 



The cover of the box where they are kept, ought to have small 

 holes in it for the admission of fresh air ; or it may be covered with 

 crape or gauze. It ought not to be too shallow ; for if so, the wings 

 of the butterfly, when it comes forth, may be bent or injured. 



We have thus seen our insect in its first stages of life ; but it is 

 destined to arrive at a higher stage of existence, and is born to be ad- 

 mired, though it does not reach this stage till it has undergone sickness 

 and suffering, with hardly any apparent sign of life. In a short time, 

 however, it awakes from its trance, and appears full of animation, and 

 is richly ornamented.* 



ON THE MIGRATION OF BIRDS. 



BY PROFESSOR TEMMINCK, OF THE UNIVERSITY OF LEYDEN. 



I SHALL here give some observations on the periodical and frequently 

 long journeys performed by several species of erratic birds, and on the 

 points of reunion and departure which they appear to select. The 

 yearlings and the old ones rarely go together in these journeys, 

 which are more or less extended, as the necessity of seeking a fresh 



* The History of the Butterfly itself will be given at a future opportunity. 



