IN MYRIAPODA AND INSECTA. 
287 
and from the enlarged condition of the latter part I at once suspected that new limbs 
were about to be produced. 
On the 10th of September 1842, a few days after the commencement of my observa- 
tions on this individual, the young Lithobius changed its skin, and, to my great satis- 
faction, not only developed two additional pairs of legs, but also reproduced three other 
pairs in the place of those that had been lost. Thus three pairs of organs were developed 
at this change, besides those which make their appearance in the usual course of 
growth. These three pairs of reproduced legs made their appearance at the sides of 
the segments, without having previously been developed in a more rudimentary form, 
as is always the case with the legs of Lithobius when first produced. But they 
were exceedingly delicate, and were much smaller than the others. They gradually 
increased in size, and continued to grow for a short time after the casting of the skin. 
The two pairs of additional legs developed at this change, and now constituting the 
eleventh and twelfth pairs of the body, were at first larger than the reproduced ones, 
and continued to grow until the next change. On the 15th of September the three 
pairs of reproduced legs seemed to have attained their maximum of development 
until the next casting of the skin, but they were not so large by one-third as the legs 
immediately anterior to them. 
On the 24th of October the young Lithobius again lost one of its legs. This 
was the twelfth one on the left side that had been developed at the preceding 
change. Nothing further took place, either in this individual or in others of the 
same age, with twelve pairs of legs, until the 7th of November, when it again 
changed its skin, and acquired three additional pairs of legs, — thus completing 
the adult number, fifteen. At this time it was nearly half an inch in length. I 
now found not only that the first reproduced legs had very nearly attained their 
proper size, but also that a new leg had been developed in the place of the one that 
was lost on the 24th of October, but this was very much smaller than the others. 
The two posterior pairs of legs, at this period, were scarcely so long as those imme- 
diately anterior to them, were applied very closely together, and were entirely use- 
less. They continued to grow in length and size, and gradually acquired a power 
of motion. On the 18th of November the posterior segments and legs in the young 
animal had nearly attained their relative proportions. On the 30th of November 
the posterior legs were widely separated from each other, and were occasionally em- 
ployed by the animal in its retrograde movements. In this condition it remained till 
the end of January, having passed the interval in a state of partial hybernation. It did 
not again change its skin until the middle of April. During this interval the pos- 
terior pairs of legs continued to be elongated, and the reproduced legs, acquired at 
the two preceding castings of the tegument, were also enlarged, but still continued 
smaller than the others. I attributed this in part to the animal not having been 
supplied with a sufficiency of food. On the morning of the 22nd of May it again 
changed its skin, and the reproduced legs had now acquired their full size. On the 
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