102 THE DEVELOPMENT OF 



Attempts to render the whole egg transparent and to 

 mount it in balsam were not very successful. 



For hardening, Perenyi's fluid, followed by successive 

 strengths of alcohol in the usual manner, was found to be 

 the best. For staining, Grenacher's alum-carmine gave 

 the best results. Kleinenberg's haematoxylon and Grena- 

 cher's borax-carmine were also used with success. It was 

 found impossible to remove the egg membranes, but the 

 reagents mentioned penetrated fairly well. Except in 

 studying the eye after the deposition of pigment had be- 

 gun, the embryos were stained entire. The eggs were 

 embedded in paraffin by means of chloroform ; the sec- 

 tions were cut by the Thoma microtome and fastened to 

 the slide with Schallibaum's collodion clove-oil mixture. 

 I do not find it necessary, in using this, to heat the slide 

 until the clove oil has evaporated, but merely enough to 

 melt the paraffin and allow the sections to drop into the 

 sticky film. The paraffin was then dissolved in turpen- 

 tine and balsam and cover glass applied. The sections 

 never became loosened. The processes involved in study- 

 ing the eye are given elsewhere and need not be repeated 

 here. 



The small size of the eggs rendered it difficult to em- 

 ploy the ordinary method of orientation and so the fol- 

 lowing process was devised : The eggs (from thirty to 

 fifty at a time) were placed in melted paraffin in a flat 

 watch-crystal, and allowed to cool. Then, on looking 

 through the glass with a hand-lens the exact position of 

 each egg could be readily ascertained, and those suitable 

 for sectioning could be cut out with a knife and mounted 

 on the plug of the microtome in any desired position. 



The drawings illustrating this paper were all made with 

 the Oberhauser camera ; in some the outlines being drawn 

 by it and the details then filled in freehand, while in oth- 



