150 FOOT AND S/'KOBELL. 



p:xplanation of plate c. 



Photo. 13. Section (4 ;u) through cytoplasm of oocyte, second order. About 

 one-third of the negative reproduced. Fixative, Hermann. Hardened in 10% 

 formaldehyde, 21 hours. Unstained. X 870. Medium, glycerine. The photo- 

 graph was taken to demonstrate the two aggregations of osmophile granules, 

 and the smaller ones throughout the cytoplasm. Cf. No. 14, which is the same 

 section, after staining in iron haematoxylin 24 hours, and dissolving out the osmo- 

 phile granules with xylol and xylol balsam. A careful comparison of the two 

 photographs will show that they are focused on the same plane, the stained prepa- 

 ration, however, showing no trace of the black granules demonstrated in the 

 unstained section. No. 14 shows that the stain has differentiated certain granules 

 that are not seen at all, or are very faintly indicated in the unstained preparation 

 The section was finally stained deeply with methyl green, with the view of deter 

 mining whether any granules could be differentiated within the vacant places 

 formerly occupied by the black osmophile granules. None could be seen. 



Photo. 14. See No. 13. 



Photo, i 5. Section (4 ^l) through upper pole of first maturation spindle. A 

 centrosome in the sphere, and equally sharply stained granules beyond the sphere. 

 Fixative, chromo-acetic. Hardened in alcohol. Iron haematoxylin. X 960. 

 Medium, xylol balsam. 



Photo. 16. Section (3^)' of egg at pronuclear stage, showing a part of one of 

 the pronuclei which have attained about one-half their maximum growth. (After 

 other fixatives, the pronuclei have a very different appearance.) Aggregations of 

 archoplasm (polar-ring substance) at periphery; possibly some of the same sub- 

 stance around the pronucleus. Fixative, .2% osmic. Hardened in 5 % formalde- 

 hyde, 22 hours. Iron haematoxylin, 28 hours. X 540. Medium, xylol balsam. 



Photo. 17. A very thick section (10 fx) of an oocyte, first order. Lower pole of 

 first maturation spindle, and an indication of the chromosomes which are approach- 

 ing the lower pole (spindle at anaphase). This section was photographed merely 

 because it showed thick rays from the attraction sphere, which strongly suggest 

 those seen in the living egg (represented in Text-fig. Ill, at a little earlier stage). 

 The sap globules in this egg are larger than is the rule in normal eggs at this 

 stage. No. 18 is the following section photographed to show the row of sap 

 globules completely surrounding the attraction sphere, and to compare this attrac- 

 tion sphere with that of Photograph 15, in which case the egg was killed in 

 chromo-acetic. Fixative, i % osmic acid. Hardened in alcohol. Iron haema- 

 toxylin. X 500. Medium, xylol balsam. 



Photo. 18. See No. 17. 



' We have tested the accuracy of our microtome by measuring the diameter of the eggs, both 

 before and after sectioning, and counting the number of sections; e.g ., this section is one ot a series 

 of thirty, and the largest of these measures 94 m in diameter. 



