CHAPTER VI. 



STUDY OF THE BLASTODERMIC VESICLE AND THE 

 SEGMENTATION OF THE OVUM. 



Method of Obtaining Blastodermic Vesicles from the Rabbit. 



The does should be allowed to become pregnant and be isolated until 

 they have littered ; the date of littering should be noted, and thirty days there- 

 after the buck be admitted and the exact time of the covering recorded. At the 

 proper number of days thereafter the animal should be killed and the uterus 

 removed at once. It may be opened with two pairs of forceps used to split the 

 outer muscular walls of the organ, beginning the operation at the lower end of 

 the uterus. With a little care this can be done without rupturing the mucous 

 membrane, which is to be afterward also opened in a similar manner with the 

 forceps and the blastodermic vesicles exposed. They are small bodies of rounded 

 form and with a brilliant pearly luster, and are easily observed. During the 

 earlier stages, which occur in the Fallopian tubes, the ova are very small and 

 difficult to find, but by the time the ovum has reached the uterus it has become 

 a blastodermic vesicle measuring about 0.6 mm. in diameter, and, therefore, 

 easily seen by the naked eye. From the fourth day after coitus until the begin- 

 ning of the seventh day the vesicles lie free in the uterus. Usually early in the 

 seventh day the vesicles, which then measure about 4.5 by 3.5 mm., begin to 

 attach themselves to the wall of the uterus, and thereafter are much more diffi- 

 cult to remove. At the beginning of the fifth day the ova measure about 0.6 to 

 0.9 mm. in diameter, but vary greatly in size, and are found more or less near 

 together in the upper portion of the oviduct. By the end of the sixth day they 

 measure about 4.0 mm. and are distributed throughout the entire length of the 

 uterus. 



The most useful stages are the vesicles from the beginning of the sixth and 

 seventh days. To preserve the vesicles they must be gently removed from the 

 uterus, great care being necessary not to injure them, and dropped into Zenker's 

 or Hermann's fluid. In either of these they may be left for about an hour and 

 then washed and preserved in the usual manner. Specimens should be examined 

 in the fresh state, just after they have been preserved, and after they have been 



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