70 



BRANCH ARTHROPODA. 



FIG. 116. 



Ci cd' da sep ten' de dm. Seventeen-year Cicada. 



smaller twigs of trees by gouging long furrows in them, 

 in which it deposits its eggs. The larvae on hatching, 



drop to the ground, 

 burrow, and suck 

 the juices from 

 roots. The Seven- 

 teen-year Cicada 

 (si ka'da) thus lives 



for about seventeen 

 years ; but finally, 

 as a pupa, comes 



to the surface of the soil, crawls up the trunk of some 

 tree, and attaches its claws. Its shell now splits down the 

 back, and the imago crawls forth. It rests for a time, 

 that its wings may expand and dry, and soon flies away. 

 Closely allied are the Aphides (an dez), the exquisite 

 little forms which gather on our house-plants.* Plant- 

 lice have a wonderful life-histgry. The eggs deposited 

 on the plants in the autumn hatch in 

 the spring asexual (a sex'u al) and wing- 

 less individuals. These produce living 

 young, likewise asexual, in succession, 

 often to the twelfth generation. At the 

 close of summer, winged and sexual ones 

 appear. These, pairing, their eggs do not hatch until the 

 following spring. This asexual method of propagation is 

 called Parthenogenesis (par the no jen'e sis). It has been 

 calculated that a single Aphis will give rise to a billion 



itself, thus producing the familiar clicking noise of the Cicada. The pupil can 

 easily make a dissection of the insect, and examine the apparatus for himself, as 

 is hoped he will frequently do in similar cases. 



* Nothing can be more amusing than to watch the plant-lice for half an 

 hour, while gorging themselves with the honey extracted from the tender bark, 

 and observe the treatment they receive from the ants, which keep them, as we 

 do cows, extracting from them a sweet liquid, of which they are very fond. 



FIG. 117. 



A' phis ro 1 see. 

 Plant-louse. (Magnified.) 



