102 The Ottawa Naturalist. [Dec. 



In the making of photomicrographs of recent or fossil 

 specimens we have to face conditions very similar to those just 

 described. The innumerable elevated microscopic grains on an 

 ordinarily rough surface catch light on their summits and scat- 

 ter it as do motes in a sunbeam. This light caught on a photo- 

 graphic plate swamps the detail which lies just under these 

 summits. If our specimen is of calcite a thin outer layer is 

 practically transparent, and with the light scattering reduced, 

 we should get some structural detail just under the surface it- 

 self. In this way we secured a view of the sutural canals of 

 Palaeocrinus striaius. Bill., and their membranous linings in 

 (1911), plate V, fig. 2, while only the canal coverings were visible 

 where the gum was not used, as in fig. 1 of same plate. Com- 

 pare also figs. 3 and 4 of this plate. In 1913 (a) plates 6 and 7, 

 we illustrated the difference in effect secured when this process 

 was used on very recent material. In same reference, in plates 

 3 and 4, we also showed the value of being able to penetrate 

 thin sheets of calcite adhering to the surface of a mold. Its 

 value in revealing features just underneath the surface was also 

 shown in 1913 (a) plate 10. Sometimes we desire just the surface 

 contours or topography, and we may then add to the reflecting 

 points by using the Williams process (holding the specimen in 

 the combining vapors of ammonia and hydrochloric acid). We 

 may thus avoid all stains or detail in colour and get pure form. 

 If, however, we are to do something more than simple species- 

 making, we should desire the detail due to difference in tone 

 or hue. For instance, in the author's work on Blastoidocrinus 

 and Paleocrinus (1911), he found internal organs outlined with 

 black and partially filled, by respiratory and alimentary pro- 

 cesses, with mud now yellow with limonite. The contrast be- 

 tween ossicle and decayed soft tissue could have been repro- 

 duced almost as pure white and black, or very like the results 

 obtained in 1913 (a), plates 7 and 8. 



The better to compare these two methods we may suppose 

 that a dM^eller on the moon desires to photograph the earth. 

 If he could but find the illuminated hemisphere covered with 

 cloud he could eliminate surface stain and get pure but very 

 general form. On the other hand, could he find a hemisphere 

 free from cloud he could get general form plus many differences 

 due to hue and tone. He would have the deeper, truer surface, 

 the detail of mountain and valley, and a very significant differ- 

 ence between sea, mountain top, Sahara and valley of the 

 Amazon. 



The ability by means of this process to reduce the amount 

 of reflection from the microscopic facets of granular surfaces 



