638 ZOOLOGY SECT. 



spicuous 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 in- 

 spection, 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 multicellular plants 

 each and every cell is capable of taking on the function of repro- 

 duction 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 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 buds, and in the buds, after they have become 

 separate, ova and sperms are developed from the cells of the ecto- 

 derm. A similar phenomenon is to be observed in other Coelen- 

 terates and in the Polyzoa and the Composite Ascidians, and also 

 in certain cases among the Platyhelminthes and Annulata. In all 

 these, and in other cases that might be mentioned, the germinal 

 substance is not confined to the reproductive cells new repro- 

 ductive cells being capable of being formed from the substance of 

 the cells of various tissue-layers. 



The phenomena of regeneration are important in connection 

 with this question of the site of the germinal substance. Many 

 members, not only of the lowest phyla, but of the Echinodermata, 

 the Annulata, the Arthropoda, the Mollusca and the Chordata, 

 are able, as has been repeatedly mentioned, to replace, by a process 

 resembling budding, parts that have been broken off : some of 



