268 W. G. VanJVanie — Embryology of Eustylochus. 



With all of these except the last three I obtained at one time or 

 another fair preparations. The chief objection to the fluids contain- 

 ing osraic acid is the difficulty of staining the eggs fixed Avith them, 

 but in addition to this the structures were usually not so well 

 preserved as with some of the other reagents. On the whole I 

 found the corrosive-acetic and picro-acetic fluids the tnost satisfac- 

 tory, and nearly all of my best preparations were preserved in one 

 or the other of these two reagents. The clusters of eggs can be 

 handled entire, but because of the thick membrane and the coating 

 of mucus surrounding the eggs the penetration of the killing fluid is 

 much interfered with, and satisfactory preparations are exceptional, 

 while a large percentage are absolutely worthless. 



The appearance of the cytoplasm and yolk in the finished prepara- 

 tion varies with the reagent used in preserving them. Most of the 

 above mentioned fluids, especially those containing corrosive subli- 

 mate, harden the yolk globules well, so that they preserve their 

 spherical shape and to a considerable extent their size. They stain 

 quite readily, both with hagmatoxylin and with plasma stains. The 

 picro-acetic fluid, however, allows the yolk spheres to shrink into 

 irregular forms and to so great an extent that the whole egg often 

 becomes greatly contracted and of irregular outline. The yolk has 

 less aflinity for stains, and the cytoplasmic reticulum, not the yolk 

 globules as in the corrosive preparations, becomes very conspicuous. 

 I have endeavored to reproduce this appearance in the drawings, 

 some of which (for example. Figs, 2, 11, 25 and 27), were drawn 

 from picro-acetic preparations. 



The masses of eggs were usually left in the fixing fluid over 

 night, washed in seventy per cent, alcohol, dehydrated and imbedded 

 in paraffin. I did not meet with any difficulty in imbedding the 

 eggs, nor in cutting them into sections "007 to -Oil™™ in thickness, 

 which was as thin as necessary. Many of the preparations could be 

 cut much thinner, 



Klinckowstrom, Francotte and Van der Stricht all found great 

 difficulty in imbedding or cutting their material, but I found no 

 unusual precautions necessary except to take care that the eggs 

 remained in each change of alcohol or clearing fluid long enough 

 to insure thorough penetration. For clearing and as a solvent for the 

 paraffin I used xylol, and my success may have been partly due to 

 the use of this medium as well as to the more favorable material. 

 For the study of the early stages, previous to laying, the entire 

 animals may be killed and imbedded, but as observed by Van der 



