FERTILIZATION OF THE FROG'S EGG 



127 



Exactly 50 minutes after the testes are first cut into pieces, "begin stripping 

 eggs from an ovulating female into tottom Petri dish marked "N". Estimate about 

 50 eggs per dish, and then strip into the "bottom Petri dish containing the next 

 concentration. A single ovulating female should provide enough eggs for the 5 

 "bottom Petri dishes. A second female will "be used for the remaining 5 top Petri 

 dish aeries. Gently rotate the dishes so that each egg is exposed to the sperm 

 suapenaion. 



After 5 minutes, flood each dish with Spring Water so that the egga are entirely 

 covered. Do not distur"b them further until three (5) hours after the time of 

 insemination. Series "A" and series "B" "below represents the top and "bottom 

 Petri dish series, or egge from two different females. 



CONCENTRATION OF 

 SPEEM 



SERIES "A" 



SERIES "B" 



100^ 



80^ 



1 1 60^ 



itO^ 



20^ 



0^ 



(D 



W (D 



(D as 

 O (D 



© o 



COMPOSITE GRAPH OF SPERM CONCENTRATIONS AND FERTILIZATION 



N 

 (Control) 



O.IN 



O.OIN 



O.OOIN 



O.OOOIN 



CONCENTRATIONS OF SPERMATOZOA 



These o"bservatlona need not be carried "beyond the l+-cell stage, or about h hours 

 after insemination. 



B. TIME AND CONCENTRATION RELATIONS 



The preceding experiment Is concerned with the dilution factor alone, in which in- 

 semination was simultaneous for all concentrations of spermatozoa. In this section the 

 factor of time Is also Involved, being superimposed upon the various sperm concentrations. 

 In this way the student can determine which of the concentrations will last the longest In 

 terms of giving highest percentage of fertilizations. 



It will be necessary to use #2 covered Stenders for this exercise. These Stenders 

 must be biologically clean and should be properly tested. The covers will tend to reduce 

 the evaporation during the longer time intervals. Secure, wash, and label 28 such Sten- 

 ders as indicated on the following table. 



