ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 263 



in each being 24 hours, and the 80 p.c. having enough iodine solution 

 to make it a deep brown colour. 



The next step is to remove silica or other mineral constituents by 

 immersing the blocks in 10 p.c. hydrofluoric acid for 3 or 4 days, the 

 acid being changed once or twice. This is followed by washing in 

 running water for 2 to 4 hours. 



The next step is to dehydrate thoroughly in graded alcohols in the 

 usual way, and remove any residual air with the vacuum pump. 



The material is now ready for impregnation with celloidin, which is 

 dissolved in ether and synthol or ether and absolute alcohol. Ten 

 grades from 2 to 20 p.c. celloidin are to be used. The blocks are placed 

 in a bottle, which can be firmly and tightly stoppered, covered with 

 2 p.c. celloidin solution, and the bottle incubated for 12-18 hours at 

 from 50°-60° C. On removal the bottle is quickly cooled in cold water, 

 after which the 2 p.c. is replaced by the 4 p.c. solution, and so on till 

 the thickest grade is reached. On removal from the last, the celloidin- 

 ised block is placed in chloroform for 12 hours, and then transferred to 

 a mixture of equal parts of glycerin and 95 p.c. alcohol. 



• Sections are best made with a sliding microtome ; for histological 

 examination a thickness of 10 /x is sufficient, but for photomicrographic 

 purposes they should be as thin as 5 /a or less. 



For staining and mounting it is usually advisable to remove the 

 celloidin at this stage by placing the sections for 10 or 15 minutes in 

 ether, and afterwards in 95 p.c. alcohol. The most useful stain is 

 hematoxylin, followed by safranin. After staining, the sections are 

 treated in the usual way, and mounted in balsam. It is advisable to 

 clear the sections in the same kind of liquid as is used for dissolving the 

 balsam. For photographic purposes the best stain is Heidenhain's iron- 

 haematoxylin. The sections should be repeatedly washed in distilled 

 water after the iron-alum and before they are placed in hematoxylin. 



In some cases it is necessary to retain the celloidin matrix ; the sec- 

 tions should then be dehydrated in a mixture of alcohol and chloroform. 



In order to make serial mounts, the sections are cut on the following 

 mixture : — Alcohol 90 p.c, 85 parts ; glycerin 15 parts. As the sections 

 are cut, they are arranged on strips of thin smooth paper, and when the 

 alcohol has evaporated the strips are turned face downwards on slides 

 coated with albumen fixative. Several layers of paper are piled on, and 

 the whole pressed down with a squeegee roller covered with another 

 slide. The lot is then clamped together and placed in an incubator to 

 dry for not more than 12 hours. When removed, the paper is stripped 

 off, and the slide with adhering section is treated in the usual way. 



Preparing and Staining the Eggs of Haminea Solitaria.* — 

 A. M. Small wood fixed the eggs with Kleinenberg's picrosulphuric and 

 Conklin's picro-acetic mixtures. In order to facilitate penetration of 

 the fixative, the capsules were torn through with wooden needles. The 

 eggs were left in the fixative for 1 hour, and then transferred to 70 p.c. 

 alcohol, which was changed until the colour due to picric acid was removed. 



For staining, Heidenhain's iron-hasniatoxylin was used, followed by 



* Bull. Museum Comp. Zool. Harvard, slv. (1904) pp. 261-318 (13 pis.). 



