No. 2.] THE EGG OF BUFO LENTIGINOSUS. 295 



Generally the eggs were found in the body cavity and oviducts 

 of the female, and such eggs were fixed at once. For the pur- 

 pose of comparison with those normally fertilized, eggs taken 

 from the lower part of the oviducts were artificially fertilized 

 by being gently shaken in a vessel of water containing small 

 pieces of testes. Young ovarian eggs were obtained in the 

 latter part of September, just before the beginning of the 

 hibernation period. 



The difficulty which many investigators have found in sec- 

 tioning and staining the amphibian Q.gg in a perfectly satisfac- 

 tory manner will, perhaps, warrant a somewhat detailed account 

 of the method by which I was enabled to obtain unbroken 

 serial sections from 4 /x to 6 /Li thick, and also to differentiate 

 sharply various parts of the ^%g. 



Killing reagents which have given excellent results on other 

 eggs — : Hermann's fluid, Flemming's solution (strong), picro- 

 sulphuric, picro-acetic, and alcoholic-acetic — cannot be used 

 on the egg of Bufo. The first two cause the eggs to disinte- 

 grate in a short time, while the others render the eggs so 

 brittle that they cannot afterwards be sectioned successfully. 

 By far the best killing reagent for the toad's Q.g% is corrosive- 

 acetic. Eggs left from five to ten minutes in a saturated solu- 

 tion of corrosive sublimate containing 5 per cent glacial acetic 

 acid, washed in 50 per cent alcohol and preserved in 80 per 

 cent alcohol, give particularly good results in the maturation 

 stages. If the amount of acetic acid is increased to 10 per 

 cent or decreased to 2 per cent, there is no marked effect on 

 the Q^g'g. It is necessary to remove the jelly-like coating of the 

 eggs within a few days after fixation, as the eggs soon disinte- 

 grate if it is allowed to remain. 



For the fertilization stages the following solution (a slight 

 modification of that used by Schultze) is recommended : 



I per cent chromic acid 25 parts 



Glacial acetic acid 10 " 



Distilled water 65 " 



Eggs are left in this solution from eighteen to twenty-four 

 hours, then washed thoroughly with distilled water and carried 



