1877.] with some notes on Protective Resemblance. 27 



profile, and its section circular; that of the Laphria is depressed, 

 but, to favour the illusion, it always arches up its abdomen both 

 longitudinally, doubling its tail beneath it, and transversely, so 

 that its section is a meniscus, Mr Albert Goodman, who executed 

 pictures of them for me, has illustrated this point. When the fly is 

 seen either from above or obliquely either fore or aft, the illusion 

 is complete, but in direct profile and from underneath the hollow 

 deception is apparent. The gay deceiver is detected. I lay some 

 stress on this device, because when the habit as well as the aspect 

 of an insect promotes resemblance we have an independent 

 witness to the teleological bearing of the imitation, and the argu- 

 ment presents itself to the mind with overwhelming force. Thus, 

 to take a parallel from the British fauna, when the larvae of the 

 larger geometrse show such a striking resemblance to a jointed twig 

 that they are called by the vulgar stick-caterpillars, and we 

 further find that they are in the habit of standing immoveable 

 with their four false legs grasping the stem of a bough, with their 

 heads and remainder of their bodies lifted freely in the air at an 

 angle corresponding to the spraying of the plant on which they 

 feed ; then the combined testimony of aspect and habit prove the 

 utilitarian nature of the likeness. 



In discussing the phenomena of mimicry Mr R. A, Wallace in 

 his book on Natural Selection (pp. 76, 77) lays down three laws 

 which govern it, and which I take the liberty of expressing in my 

 own words. 



In all cases of true mimicry 



1. The imitated and imitating species are to be found in the 

 same country, situation, and at the same season. 



2. The imitated species (or group of species) are abundant in 

 individuals, have a wide range, and are ascertained to have some 

 special protection. 



3. The imitating species have a less number of individuals 

 and a more restricted range than the imitated. 



These laws are connected by the theory, that the imitating 

 species, by virtue of its resemblance, shares the advantages of the 

 special protection of the imitated species by not suffering from the 

 attacks of enemies who have acquired or possess the instinct to 

 avoid the imitated species. 



This instance conforms well to these laws, 



1. In identity of position, since I caught both repeatedly in 

 the same place at the same hour. 



2. The imitated species is a dominant species. It is found 

 all round the shores of the Mediterranean, and -extends through 

 Upper Egypt, Syria, and Arabia into Hindostan, and is one of the 

 most common of insects in those countries. It has a special pro- 

 tection, since it is one of the largest and most formidable of the 



3—2 



