HISTORY OF THE LARVAL AND PUPAL STAGES. el ¥4 
of growth will vary considerably in size of the body and the softer 
parts, representing perhaps a difference in age in some cases of one 
or two years, but the hard parts will present a very uniform size and 
character. 
The peculiar structure of the enlarged anterior legs furnishes per- 
haps the best means of distinguishing the adolescent stages of this 
species from other cicadas and the modification which these limbs 
undergo with the different molts the best means of determining the 
age of the larve. The peculiarities of the anterior legs consist in the 
enormous enlargement of the femora and tibiz and their development 
into structures which resemble somewhat the cutting mandibles of 
biting insects or recall the fossorial forelegs of the mole cricket. The 
peculiar structure of these legs is in fact especially designed for dig- 
ging, tearing, and transporting earth in the course of the insect’s sub- 
terranean life. As already indicated, the amount of burrowing in 
the early stages is not necessarily very great in any one year, but dur- 
ing the entire seventeen years conditions may occasionally arise which 
will demand a considerable activity on the part of the young Cicada. 
The details of the structure of the front legs, which are given in the 
technical description of this species, are quite characteristic and 
diverge notably from the similar parts of other species. The anterior 
tarsus of the periodical Cicada exhibits also a rather peculiar meta- 
morphosis during the adolescent life of the species. In other words, 
during the first larval stage and in the pupal stage it is similar to the 
other tarsi but considerably longer, being attached to the inner side 
of the greatly enlarged tibia and at a considerable distance from the 
clawlike tip of the latter. The fore tarsi are of service to the young 
larva in walking and climbing and in the same way to the pupa after 
its emergence from the soil, facilitating its climbing trees or other 
objects; in other words, covering the periods between the hatching 
and entering the soil and between the emergence of the pupa and the 
disclosure of the imago. During its long subterranean life, however, 
these long, slender tarsi, being distinctly in the way in digging in the 
earth and of no service, become rudimentary with the first molt and 
nearly disappear in the subsequent larval stage. They reappear in 
the first pupal stage, but in this and the subsequent pupal stage, 
while the insect is still below the soil, they are folded back along the 
tibiz, so as to be practically functionless (see fig. 51), and are only 
unfolded and brought into service after the pupa has emerged from 
the ground. 
The more detailed description of the different stages which follows 
will facilitate the easy recognition of any particular stage. The chie! 
points to be considered in determining both the age of the larva anc 
whether or not it belongs to the periodical species are the measur: - 
ments of the corresponding parts of the legs and antenne, but pc 
