i6o STUDIES IN THE EVOLUTION OF ANIMALS 



which have given them their general colour, that is, from an 

 ancestry in which' plate-armour had been established for ages. 



I would repeat that the spotting is the important feature, and 

 not the colour of the spotting — for we see in the Cheetah, black 

 spots on a light ground, and in the Deer, white spots on a dark 

 ground, and in the Kerry Cattle we see a white spinal line, instead 

 of the ordinary dark one. The reader .might say — Is it reasonable 

 to suppose that an armour-plate should leave an impression after 

 the bony plate had totally disappeared, and should continue to be 

 pictured in the descendants for innumerable generations? It does 

 seem strange that this should be so, but impressions are left from 

 far more transient causes than the carrying of bony plates on one's 

 skin for perhaps millions of years. 



Mr. W. B. Croft, in a communication to the Physical Society, ^ 

 has shown that impressions of coins can somehow be left on a 

 clean glass, invisible at first, but made visible by breathing on the 

 glass ; also that an impression of a paper, printed only on one side, 

 can be invisibly taken by pressing it between two plates of glass. 

 The printing can be brought out by breathing on the glass which 

 was opposed to the printing. What is more curious is that a 

 similar print-impression is given to the glass which does not face 

 the printed surface. This latter impression can also be brought 

 out by breathing over the glass surface, and it is evidently 

 produced through the paper. Presumably light may have some- 

 thing to do with these impressions. But if so slight and temporary 

 an influence can leave an impression on the glass, what wonder 

 would it be if the armour-plating, carried for who knows how many 

 ages, should have so modified the skin, and its nerve-centres, as to 

 transmit '^XzXe-pictures, even when the calcareous plates had totally 

 disappeared ? 



^ Reproduced in Year Book of Science for 1892, p. 16. 



