ZOOLOaY AND BOTANY^ MICKOSCOPY^ ETC. 147 



mostly very large prej)arations a small diaptragm cannot be used 

 and hence there is too much light, which drowns the images. Stained 

 preparations in balsam are for the most part unsuitable, and glycerin 

 preparations must be very thin, and are therefore difficult to make of 

 the necessary size. The difficulty may, however, be got rid of by 

 placing the sections direct from the microtome in a solution of nitric 

 acid 1 part, water 15 parts, and there leaving them until they are 

 a dazzling white. They should then be mounted in glycerin without 

 previous washing. Thus prepared the sections, even though not 

 very thin, are not only in an admirable condition for the Sciopticon, 

 but in the case of microscopic or low-power examinations, will be 

 found to give sharper images than by any process hitherto known. 



The author has also found the Sciopticon useful as a means of 

 drawing large sections under low powers. For this purpose the 

 nitric acid preparations are very suitable, as all the details are thrown 

 on the drawing-paper with marvellous clearness. 



Treatment of the Ova and Embryos of the Aphides.* — E. 

 Witlaczil publishes a lengthy paper on the development of the 

 Aphides, and gives the following information on methods : — 



The embryos of the viviparous aphides were examined in a weak 

 salt solution (1^ per cent.), in which they live for about an hour. 

 The ovaries contain embryos in different stages of development, and 

 have to be isolated for study. 



The early stages in the development of the ova may be studied to 

 advantage after treatment with hydrochloric acid (3 per cent.) or 

 acetic acid, as these reagents partially dissolve the yolk elements and 

 thus render the preparation more transparent. The later stages, on 

 the contrary, are rendered more opaque by the same treatment. 



Preparing Echinorhynclii. — In the paper by A. Safftigen already 

 noted,| the following methods of preparation are described; — 



It is a very difficult matter to kill EcIiinorJiyncM instantly. This 

 cannot be done either with corrosive sublimate or strong osmic acid, 

 even after preliminary treatment with tobacco smoke or chloroform. 

 Thus treated, they contract strongly, and remain so after death. 



Much the best results are obtained by killing gradually with • 1 

 per cent, osmic acid, in which they contract during the first hours, but 

 stretch out again and die fully extended. This method causes slight 

 swelling, but does not seriously injure the object for histological 

 investigation. In specimens left for twenty-four hours in the osmic 

 acid, it is easy to isolate under the dissecting Microscope the subcuti- 

 cula and the two layers of muscle-fibres (circular and longitudinal). 

 For the study of the internal organs, the EcMnorhyncM should be cut 

 open immediately after death and transferred to a O'Ol per cent 

 solution of osmic acid. The preservation of specimens thus treated 

 may be accomplished in the following manner: — After carefully 



* Zeitschr. f. Wiss. Zool., xl. (1884) pp. 559-696 (7 pis.). Abstract, supra, 

 p. 53. 



t Morphol. Jahrbuch, x. (1884) pp. 120-71 (4 pis.). See this Journal, iv. 

 (1884) p. 897. V ^ f i- K f J 



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