THE CYCLE OF LIFE 457 



There is a rather famous Aphis — Schlechtendalia chinensis 

 — ^which makes galls on Rhus semi-alata in Japan and 

 China. The galls are used in dyeing and tanning — ^they 

 are rich in tannin, and in former times they served the 

 Japanese women as a tooth-powder for blackening their 

 teeth. Sasaki has almost cleared up its comphcated hfe- 

 history. There is a succession of wingless females, partheno- 

 genetic and viviparous, and after a time winged females 

 appear which lay eggs containing well-advanced embryos. 

 These develop into wingless females again. No males 

 have been found, and we have a ghmpse of a possible 

 continuous Parthenopeia. 



Sometimes the hfe-cycle is long drawn out, as in the case 

 of the seventeen-year cicadas {Tibicina septendecim), well 

 known in the United States, where they are often called 

 ' locusts '. (A small British relative, Cicadetta montana, is 

 sometimes found in the New Forest.) The pecuharity 

 of the Cicada is that it is specially abundant every seven- 

 teenth year in the northern States, or every thirteenth 

 year in the southern States. The eggs are laid on the 

 twigs of trees ; the larvse drop to the ground and cluster 

 on the roots, sucking the sap ; after a prolonged larval 

 period, there is short pupation, and a broad, black insect, 

 with reddish nervures on its wings, emerges. The loud 

 instrumental music or stridulation made by the males is 

 very famihar. 



Tunicates. — ^The majority of Tunicates, belonging to 

 the Ascidian type, are somewhat nondescript marine 

 animals, of sedentary habit, often compared to wine-skins 

 or leather water-bottles. Until their development was 

 made known, no one suspected that their relationships 

 were with backboned animals. The egg develops into a 



