gi6 Nichtgehaltcne Vorträge. 



is appropriated in part. With regard to internal work, some of 

 the tissues in animals and plants are costly. A time comes when 

 these may have to be sacrificed to produce a new, and for the 

 time, a more usefal material. The sacrifice is sometimes made, 

 The eyes of the blind fish of the Californian coast, and those of 

 the fish sc. in the Kentucky cave are used up in making sensitive 

 skin sense organs which are more useful in the dark. The deve- 

 lopment of animals is arrested when the surroundings do not serve 

 sometimes to excite the developmental products. Tadpoles are 

 sometimes delayed, so are axolotls. It is not uncommon for one 

 tissue to be absorbed and a new tissue deposited. Fats can be 

 converted into sugars in animals and plants, and sugars into fats. 

 The tadpole's tail is absorbed and used up in making new parts. 

 There are numerous instances of new parts being produced in 

 plants and animals, as has been mentioned. Alteration of habits 

 has been gone into by Darwin and many others, to this M. 

 Cuenot adds other and interesting examples involving the 

 production of new species very rapidly, and this all due to environ- 

 ment or rather the power of conforming to environmental changes. 

 C. Darwin takes Saurophagus sulphuratus (a fly-catcher of 

 South America) , Parus major (A titmouse) , and an American black 

 bear, that change their habits. The habits of the woodpecker 

 vary. There are, of course, several other examples, Birds with 

 web feet that avoid water etc. M. Cuenot seems to think that 

 the phenomena may be hurried up, if we have the right environ- 

 ment, and the right kind of animals. Then the Physicist may not 

 be in conflict with the Geologist and Zoologist in the matter of 

 time for the production of, at least, some forms. It may be that 

 less time would be required if all conditions were fulfilled. But 

 Darwin has given instances where breeding produced in a 

 comparatively short time animals of a very special nature. We 

 know, indeed, that whatever is given out to be the fashionable 

 colour sc. of dogs will lead in a few years to their production by 

 selection. The „points" about the English sheep-dog were changed 

 a few years ago, and a new lot of dogs were soon placed before 

 the public. The success of trainers furnishes us with hopes that 

 animals will be found that are keener to modify themselves than 

 any we have. ,,According to our experience", says Darwin, 

 „abrupt and strongly marked variations occur in our domestic 

 production, singly and at long intervals of time. Yet he was of 

 opinion that we have no right to assume that in the past many 

 of the species were suddenly formed. Few would be willing to 

 admit sudden modifications, but must one necessarily admit that. 

 all forms much specialized are terminal, seeing that the embryoes 

 of many animals are much more general in type than the perfect 

 form. Instinctive habits may be compared with chemiotactic 

 habits or perceptions, and in the construction of spherical nests, 



