058 ZOOLOGY sect. 



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, 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 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 multi- 

 cellular 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 ca.ses 

 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 

 substance can be shown to be widely diffused throughout the 

 plant. Thus in many flowering plants, if we cut a shoot into 

 lengths, the pieces are all capable of giving rise under suitable 

 treatment to complete plants with flowers containing reproductive 

 cells ; and in many cases a leaf, or a portion of one, is capable of a 

 similar development. In many animals a similar wide distribution 

 of the germinal material may be shown to prevail. This appears 

 most strikingly in forms that multiply by budding. In Hydra, for 

 example, any part of the body seems capable of giving off bud.s, 

 and in the buds, after they have become separate, ova and sperms 

 are developed from the cells of the ectoderm. A similar 

 phenomenon is to be observed in other Coclenterates and in the 

 Polyzoa and the Composite Ascidians, and also in certain cases 



