886.] 



MICROSCOPICAL JOURNAL. 



131 



f- 

 /• 

 /• 



20. Arthrodesmus: 



Cytioderm smooth {a^ . 

 Cytioderm verrucose or spinous {b) . 

 Semi-cell widi two spines (c). 

 Semi-cell with more than 2 spines ((/). 



Cytioderm with deciduous spines Rauii, 9^; 



verrucose in rows, margins crenate . . . qtiadridens^ 96 

 Spines on the same side diverging {e) . 

 " parallel (y) . 



converging . . . . ' . . convergens^ 9^ 

 Margin of semi-cell angular, each angle with i or 2 spines, octocornis^ 97 



End truncate : spines widely divergent Inciis. 97 



End convex ; spines moderateh' divergent . siibiilatiis. 96 ; ovalis. 96 



Nuclei, 2 in each oblong-oval semi-cell fragilis. 9^ 



Nuclei none; semi-cell oval, diameter y^U^. in. (20/) . . ovalis^ 96 

 " semi-cell orbicular, diameter yg'iiTr (i2y), orbictilaris. 96 



" semi-cell elliptical ; spines often very short, 



convergens var., 95 

 I To be co?ittnued.'\ 



Photo-Micrography. — VII. 



BY THE EDITOR. 

 [ Continued from page gj. 1 



4. Developing (continued). 



b. Pyro or Alkaline develop- 

 ment. 



Prepare the developer according to 

 any of the formulas given last month, 

 or follow the directions given by the 

 maker of the plates that are used. 

 Doubtless, however, many will pre- 

 fer to buy a developer already mixed, 

 such as that of the Eastman Dry 

 Plate Co., of Rochester, or. one that 

 we can most highly recommend, 

 which was forgotten as we wrote last 

 month, Walmsley's developer, which 

 can be obtained from Messrs. Walms- 

 ley & Co. in Philadelphia. There 

 are several others on the market, 

 which from the way they are adver- 

 tised might lead one to sujDpose they 

 are everlasting — one, indeed, is said 

 to work constantly without anv addi- 

 tion. Well, ricn d' i/nposs/ble. but 

 it is just as well for the beginner to 

 use well-tried, even though less eco- 

 nomical, preparations. 



Having mixed the solutions, pour 

 them over the plate, and constantly 

 tip the tray to make the developer 

 flow back and forth. In a few sec- 



onds the picture will appear, and de- 

 velopment must be continued until 

 details are out. Then wash thoroughly 

 and put the plate in the alum solution 

 (fomula S), which should have the 

 oxalic acid added to it for the purpose 

 mentioned. In ten minutes wash the 

 plate again, and place it in the fixing 

 solution. 



When fixed wash verv thoroughly 



I and dry. 



Treatment of plates not properly 



I exposed. 



When a picture develops all over, 



I without sufficient contrast between 



I the lights and shadows, it appears flat, 



I and the plate has been exposed in the 

 camera too long. If, on the other 



1 hand, the lights and shadows are ex- 

 aggerated, and details in the shadows 



! cannot be brought out, the plate 

 has not received sufficient exposure. 

 The former error can be remedied to 

 a considerable extent in develop- 

 ment. For the latter, not much can 



i be done. 



In attempting to modifv the course 



I of development it should be consid- 

 ered that : — 



I . A weak developer acting slowly 



j gives a soft, even development with 

 good density. 



