136 FOOT AND STROBELL. [Vol.11. 



30 minutes, the same globules are again sketched to illus- 

 trate the effect produced by the fixative (Text-fig. VI, B). A 

 comparison of Text-figures VI and VII will show the relative 

 injury to the form of the globules produced by i^ osmic acid 

 and chromo-acetic. Photo. 3 further illustrates the effect of 

 chromo-acetic on the sap globules and a comparison of this 

 Photo, with Photos. 2 and 5 will show that osmic acid and 

 corrosive sublimate are far less injurious. In Photo. 2 many of 

 the sap globules in the center, and the line of globules on the 

 right, were sketched from the living egg (camera lucida), and 

 a comparison of the sketch with the photograph shows scarcely 

 perceptible change in structure. Such changes as occur later 

 in corrosive sublimate and osmic preparations are probably pro- 

 duced by the alcohols and imbedding. In order to test this 

 we have fixed, stained, hardened, and cleared eggs under a 

 Zeiss 2 mm. immer., oculars 2 and 4. We have repeated 

 many times each step in the technique, selecting, as in the 

 case when the fixative alone was tested, a definite number of 

 sap globules upon which to center our attention. As, how- 

 ever, the egg becomes more opaque during the process of hard- 

 ening, this method does not promise to be as satisfactory as a 

 complete comparison of sections with freshly fixed material of 

 the same stage. The above-mentioned method of applying the 

 fixative while focusing on the periphery of the ^^g (under such 

 gentle pressure that the ^gg continues to develop normally) 

 has been supported by applying the fixative to a thinner layer 

 of cytoplasm, obtained by gently pressing an ^gg until it is 

 flattened to the outer membrane. The form of the sap globules 

 remains unchanged under this pressure, and their reaction to 

 the fixative appears to be the same as when the egg is not sub- 

 jected to pressure. Whether any part of the sap globules 

 becomes coagulated by the fixatives and takes part in forming 

 the network seen in some sections we are unable to determine. 

 If the globules are present in any form, they do not stain, 

 for the vacuoles seen in the sections (Photos. 6, 16-18) un- 

 doubtedly answer to these structures. How far the breaking 

 or fusing of the sap globules may be responsible for definite 

 features of certain fixatives we are not prepared to answer until 



