290 THE ZOOLOGIST. 



natural conditions ;* whereas we should think not of years but of 

 geological epochs, for time is only an imaginary quantity, alike 

 useful to the mathematician and historian, a result of expressing 

 the term of our short lives. Thus we may seek to multiply the 

 years of our fugitive existence into a product which shall repre- 

 sent the limits of an unknown past, whilst we can only imagine 

 space by the equivalent of time. 



We have already ventured some suggestions on the subject 

 of assimilative colouration, and we now approach a different 

 class of phenomena, where the resemblance is not of colour alone, 

 but also frequently of structure, by which animals exhibit a close 

 resemblance to some inanimate object, and to which the term 

 " Protective Imitation of Particular Objects " has been aptly pro- 

 posed by Mr. Wallace, t One of the most striking examples is 

 found in the Orthopterous family Phasmidce,l and in what are 

 generally known as the " Walking-stick insects." To use the 

 graphic and accurate description of Mr. Wallace : — " Some of 

 these are a foot long, and as thick as one's finger, and their whole 

 colouring, form, rugosity, and the arrangement of the head, legs, 

 and antennae, are such as to render them absolutely identical 

 in appearance with dead sticks. They hang loosely about shrubs 

 in the forest, and have the extraordinary habit of stretching out 

 their legs unsymmetrically, so as to render the deception more 



* Mr. Sedgwick is of opinion that there is much to be said for the view 

 that the greater part of evolutionary change had already taken place in pre- 

 Cambrian times before the fossiliferous period. " If this view was correct — 

 and the probability of it should be borne in mind — the main part of the 

 evolution of organisms must have taken place under totally different con- 

 ditions to those now existing, and must remain for ever unknown to us." 

 (Proc Fourth Internat. Congr. Zoology, Cambridge, 1898, p. 75.) 



f ' Darwinism,' p. 202. — Mr. Skertchley distinguishes " protective re- 

 semblance " as copying stationary objects, and "mimicry" as simulating 

 moving ones (Ann. & Mag. Nat. Hist. ser. vi. vol. iii. p. 478). 



I Some Phasmas vary in colour in the same species, as noticed in 

 Mauritius. Cuvier was not unobservant of these peculiarities, as, referring 

 to the Phasma rossia, from the South of France, he describes it as either of 

 a yellow-green or greyish brown. (Quoted by Nicholas Pike, ' Sub -Tropical 

 Eambles,' p. 164.) It is interesting to note a superficial parallelism in 

 structure in the Skeleton- Shrimps (Caprellidce) with the Phasmidce, and in 

 Mantis- Shrimps (Stomatopoda) with the Mantidce, of which a good example 

 may be found in the Squilla mantis, BondeL 



