Page:Science vol. 5.djvu/555

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��tional Tacls in natural history always provoke scepticism, and the facia recorded regarding our dcada's liy[>ogeai) life have shared in this tendency. Hence a few facts, especially such lis bear on the development of the larva, will not prove uninteresting.

Of the tredecim brood which appeared in ISeS, I have taken pains to follow the larval development as far as possible from year to year, my observations having been made in Si. Louis county, Mo. Repeated efforts to rear the young larvae in confinement proved unsuccess- fiil ; and it was necessary to resort to careful and repeated digging oiit-doors in order to watch the growth from year to year. One of my employees at Cadet, Mo., has also been in- structed to carefully pursue the same subject, and I have repeated the digging since residing in Washington. These observations have in all cases been made in special localities where the date of entering the ground was well known and observed. I have thus been able to follow the larvae for the first six years with great care, and for subsequent years with less care and continuity. As we might expect from the clironological history of the species, the devel- opment of the larva is extremely slow ; and at six jcara old it has hardly attained one-fonrih of its full size. Notwithstanding this slow development, moulting takes place frequently i i.e., the number of larval stages is more than one per annum, and probably twenty-flve or thirly in all, whereas in the Homoptera gen- erally — the suborder to which Cicada belongs — it langes from two to four. In any hypo- gean insect which continually uses its claws in burrowing, the need of shedding and renewal of those organs ia apparent, and may afford the chief explanation of this repeated exuvia- tion, though the slow development ia a factor ; since my own experience has shown, in the larvae of other orders, that, in proiwrtion as development is slow, exuviation is frequent. As the claws of the front tibiae are the chief in- struments used in burrowing, the tarsi become useless or obstructive, and are gradually re- duced, and finally lost. They are then regained suddenly during one of the later moults, biitso articulated that they are thrown back on the inside of the tibiae, and form a good brace for strengthening these. They ai-e thus out of the way for underground work, and come into use, with their well- preserved claws, only when the pupa issues from the ground, and ascends for the final change.

Much dilTereDce of opinion has been ex- pressed by different writers as to the food of the larva ; and this is not to be wondered at.

��from the fact that there is great difficulty in observing it feed. Dr. G. B. Smith insisted that it obtained its nourishment from the moisture of the earth, through capillary haira at the tip of the proboscis ; while many others have seen it with its beak inserted in the roots of trees, and pumping the sap therefrom. The foi-raer method is insisted on by Dr. Smith from his own observations ; but while I think it not impi'uhable, es|>ecially during its earlier larval life, that the cicada may feed on earth- exudation, — a belief which receives support from the well-known fact that this cicada will issue from ground that has been cleared of timber and cultivated for nearly seventeen years, and that other species are known to issue from the prairies, — the liquid is evidently pumped up in the ordinary way. The truth of the mailer seems to be that the cicada larva can and does go for long periods without nour- ishment, where such fasting is necessitated ; and that in the earlier years of its development, more particularly, it feeds on the rootlets or radicles, not only of trees, but of herbaceous plants. In my own observations I have rarely found it more than two feet below the surface during the first six or seven years of its life, and almost invariably in an oval cell, and more often away from roots than near them ; yet I have also found it with beak inserted, and it will often hang fast by the beak after being unearthed. That the larva is capable of going to great depths is well attested by observers. Many of such reports may be based on the unobserved tumbling of the larva from higher levels ; but, where the insect has been observed to issue from the bottoms of cellars ten feet deep, the information would certainly seem to be reliable.

The method of burrowing and making its cells is quite interesting. With the strong front tibial claws it scratches away the walls of its cell just as one would do with a pick; and if it is rising, so that the earth removed naturally falls to the posterior end of the bur- row, it simply presses the detached portions on all sides, and especially on the end of the cavit}', by means of its abdomen and middle and hind legs. If, however, it ia burrowing downward, and the loose soil has to be pressed against the top of the cavity, it uses its broad front femora very dexterously in making a little pellet of the soil, and in placing it on the clypeal or front part of the head, when the load ia carried up, and pressed against the top of the cavity. The motions made in cleaning its fore-arms remind one very forcibly of those made by a cat in cleaning ita aa.^«s^M3»-

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