620 ZOOLOGY SECT. 



including sometimes the development of special excrescences or 

 appendages. In some cases of protective resemblance the colour, 

 and even the markings, change with a change of the surroundings. 

 For details of such cases reference must be made to special works. 

 Many Insects present elaborate markings which give them a close 

 resemblance to a tuft of lichen or moss, a twig, a leaf, or other 

 object, and resemblances of an equally striking character occur in 

 other classes. 



Some animals, more especially certain Insects, are protected by 

 their nauseous character against being devoured by aninals that 

 would otherwise prey upon them ; but often, no doubt, such 

 nauseous Insects are attacked and killed before their unpalatable 

 character is detected. It is thus manifestly of advantage to 

 such animals that they should be readily recognisable, and should 

 thus be passed over : and in many such cases the coloration is 

 bright and conspicuous, or the animal is rendered conspicuous by 

 other means (warning characters). 



By mimicry is meant a superficial resemblance borne by one 

 animal to a member of a different group. The best-known 

 examples of mimicry occur among the Insects. It is manifestly 

 of advantage to a Butterfly belonging to a group which is not 

 nauseous to be readily mistaken for a nauseous form with conspi- 

 cuous warning colours and markings, and this appears to be the 

 explanation of many cases of mimicry. Similarly, a variety of 

 flower-frequenting Dipterous Insects which have no sting or 

 other weapon, bear a remarkable resemblance to Bees or Wasps, 

 belonging to a distinct order (the Hymenoptera) the resemblances 

 embracing, not only shape, colour, and markings, and development 

 of hairs on certain parts, but the movements of the wings and 

 other parts and the humming sounds emitted, so that, on a 

 superficial inspection, the mimicry appears complete. 



Heredity. The various characteristics of a plant or animal are 

 transmitted, with or without modifications, to the succeeding 

 generation. 



In the highest groups of animals this transmission is effected 

 only through the intermediation of the sexual cells ova and 

 sperms since they alone are capable of giving rise to a new 

 generation. But in lower organisms the faculty of reproduction is 

 more widely diffused among the component parts ; in some lower 

 multicellular plants each and every cell is capable of taking on the 

 function of reproduction and giving rise to progeny similar in all 

 respects to the parent ; in other words, every cell in such cases 

 must contain germinal substance. In other, somewhat higher, 

 forms the germinal substance, though still widely diffused, may not 

 be present, or capable of becoming active, in all parts, and may be 

 confined to the cells of one or other of the layers. In the 

 vegetable kingdom, even amongst the highest forms, the germinal 



