PASSIVE DEFENCE 345 



the surrounding surface. When frightened, it attempts to avoid 

 discovery by feigning death, with outstretched legs, depressed 

 body, and closed eyes. If further molested, it buries itself with 

 great quickness in the loose sand. This Lizard, from its flattened 

 body and short legs, cannot run quickly." Similar observations 

 have been made as regards some Amphibians. 



Spiders are notorious for the way in which they simulate death, 

 drawing in their legs and remaining perfectly motionless until an 

 opportunity of escape offers. The same habit is characteristic of 

 many Beetles. 



FECUNDITY OF ILL-DEFENDED ANIMALS 



Many comparatively defenceless animals are extraordinary fer- 

 tile, and this may be looked upon as a special means of defence for 

 the species (which might otherwise become extinct), though it is 

 of no service to the individual. A great many ill-defended forms, 

 indeed, would seem to have as their chief function the furnishing 

 of a food-supply to other animals. The astonishing fertility which 

 compensates for such ravages has enabled many such weak crea- 

 tures not only to hold their own, but actually to become the most 

 abundant species on the face of the earth. The Rodents, among 

 Mammals, furnish a good example of this. They are the most 

 cosmopolitan of their class (with the possible exception of bats), 

 and are represented by a very large number of species and an 

 enormous number of individuals. Yet these creatures are mostly 

 of small size, and are exposed to the attacks of innumerable 

 enemies against which they are not particularly well defended. 

 On the average, it may be said that the total number of individuals 

 of any particular rodent remain fairly steady, i.e. the ravages of 

 enemies prevents the rapid production from having any marked 

 effect; but how largely such animals help to feed more powerful 

 forms has been demonstrated by cases where, for some special 

 reason, the toll levied upon them has been lessened. The Rabbit, 

 for example, is proverbial for its rapid powers of increase, not- 

 withstanding which its numbers in this country appear to remain 

 much about the same from year to year. But when this same 

 animal was introduced into Australia, a country comparatively free 

 from predaceous forms, it multiplied with such enormous rapidity 

 as to become a serious nuisance to mankind. In Europe all this 



