150 Edward Hindle 



a) ARNOLD'S Method : Mordant the sections for ten minutes in a 

 dark brown solution of Iodine and Kl in 70% alcohol. Rinse in 70% 

 alcohol and stain for two hours in a saturated solution of Basic Fuchsin 

 in 75% alcohol. Wash in water and then stain for ten minutes 

 in a 1% aqueous solution of Polychromatic Methylene Blue. Rinse 

 with water and pass up rapidly through the alcohols into a satur- 

 ated solution of Orange G in clove oil. Allow the sections to differ- 

 entiate in this solution until they appear more pink than blue, then 

 wash in clove oil, followed by xylol, and mount in Canada Balsam. 



b) HEIDENHAIN'S Haematoxylin Method (slightly modified). Mord- 

 ant the sections for ten minutes in an alcoholic solution of Iodine 

 in Kl. Then mordant in a 3.5% aqueous solution of iron alum for 

 about twelve hours. Stain for an equal length of time in a 0.5% 

 aqueous solution of haematoxylin, artificially ripened by the addition 

 of a few drops of lithium carbonate solution; then differentiate and 

 mount in the usual way. 



c) MALLORY'S Phospho-Tungstic Haematoxylin Method. Mordant 

 the sections for ten minutes in a 0.25 % aqueous solution of potassium 

 permanganate. Rinse in water and clear in a 5 % aqueous solution 

 of oxalic acid for twenty minutes. Wash thoroughly and then stain 

 for twelve to twenty four hours in a solution of phospho-tungstic 

 haematoxylin. Rinse in water, pass up rapidly through the alcohols 

 into xylol, and mount in Canada balsam. 



ARNOLD'S stain was found to give the most reliable results but 

 for the sake of comparison sections were stained by all three me- 

 thods. 



The experimental part of the work was performed at the Herz- 

 stein Research Laboratory, Pacific Grove, under the direction of Pro- 

 fessor LOEB, without whose assistance and kindly criticism it would 

 have been impossible to complete this study. The cytological exam- 

 ination of the eggs was completed in the Zoological Department of 

 the University of California, with Professor KOFOID, to whom it gives 

 me great pleasure to express my indebtedness for much help received 

 in this part of the work. 



External Changes after Artificial Fertilization. 



Under a low power of the microscope the unfertilized egg of 

 S. purpuratus appears as an opaque spherical body about 60 p in 

 diameter. During treatment with butyric acid it presents no morpho- 



