46 ON PLANTS AND INSECTS. [LECT. 



in Pyrophila tragopoginis, which feeds on the leaves 

 of the "John Go-to-bed at Noon" (Tragopogon). But 

 you will find that the smallest caterpillars rarely possess 

 these white streaks. As regards the second point 

 also, the streaks are generally wanting in caterpillars 



FIG. 35. Aryc yalathea. 



which feed on large-leaved plants. The SafyrickB, 



on the contrary, all possess them, and all live on 

 grass. In fact we may say, as a general rule, that 

 these longitudinal streaks only occur on caterpillars 

 which live on or among narrow-leaved plants. As the 

 insect grows, these lines often disappear on certain 

 segments, and are replaced by diagonal lines. These 

 diagonal lines (Fig. 36) occur in a great many caterpil- 

 lars, belonging to the most distinct families of butterflies 



