to become aware of the danger, and thrashed about the end of its body repeatedly in great alarm. But the tubes were not protruded, as I was clearly able to see with my lens. The ant saved the larva, and it is probable that ichneumons would in no case get an opportunity to sting so long as such vigilant guards were about. It strikes me that the larvæ know their protectors, and are able and willing to reward them. The advantage is mutual, and the association is friendly always.” Those who are familiar with Mr. Belt’s description of the standing armies of ants kept by the “bull’s-horn thorn” (“Naturalist in Nicaragua,” pp. 218-222) and by certain _Cecropiæ_ and _Melastomæ_, will be struck with the analogy between these and the foregoing case. R.M.] [130] [The adaptive resemblance is considerably enhanced in _Catocala_ and in _Lasiocampa Quercifolia_ by the row of fleshy protuberances along the sides of these caterpillars, which enables them to rest on the tree trunks by day without casting a sharp shadow. The hairs along the sides of the caterpillar of _Pæcilocampa Populi_ doubtless serve the same purpose. (See a paper by Sir John Lubbock, Trans. Ent. Soc. 1878, p. 242; also Peter Cameron, _ibid._, 1880, p. 75.) It is well known to collectors that one of the best methods of finding the caterpillars of the _Catocalæ_ is to _feel_ for them by day on the barks of their respective food-trees, or to beat for them at night. R.M.] [131] [See Wallace’s “Contributions to the Theory of Natural Selection,” 1st ed., p. 62. Also a paper in “Ann. Mag. Nat. Hist.” Feb. 1878, p. 159, for cases in point. Rösel in 1746 mentioned this habit in _Calocampa Exoleta_. Hermann Müller has recorded many other similar instances on the authority of Dr. Speyer; see “Kosmos,” Nov., 1879, p. 114. R.M.] [132] [Andrew Murray called attention to this fact in 1859 (“Edinburgh New Philos. Journ.,” Jan., 1860, p. 9). This view is also corroborated by the fact that no internal feeders are green; see note 142, p. 310 and Proc. Zoo. Soc. 1873, p. 159. R.M.]