CHAPTER XXV. 263 



Mammalia. * 



584. Times for Early Development. The entry of the sperm into 

 the egg of the mouse takes place from six to ten hours after copula- 

 tion (SoBOTTA, Arch. mikr. Anat. Bd., 45). The pronuclei stage of 

 fertilisation is found from eighteen to twenty-two hours, two-cell 

 stage twenty-six hours, four-cell, fifty hours, eight-cell, sixty hours 

 after copulation : the egg remains in the tube about eighty hours. 

 J. A. LONG and E. L. MARK (Contrib. Zool. Lab. Museum, Harvard, 

 Carneg. Inst. Wash., No. 142, 1911) find in the mouse that ovarian 

 eggs within fifteen or sixteen hours after parturition have formed 

 the first maturation spindle. Fertilised eggs are obtained from 

 animals killed between twenty-three and thirty-one hours post 

 partum. The time required for the spermatozoa, after introduction 

 into the uterus (either artificially or by coitus) to reach the eggs in 

 the first part of the oviduct varies from four to seven hours in mice 

 inseminated about the same number of hours post partum. To 

 obtain free eggs for study, Mark and Long kill mice fourteen to 

 seventeen hours after parturition, the ova being found in a fold of 

 the oviduct. 



In the rat the eggs are found in the oviduct about 18-7 hours 

 and ovulation occurs in less than eighteen hours post partum. 



In the rabbit the pronuclei stage of fertilisation occurs about 

 fourteen hours, in the guinea-pig, twenty-two to twenty-four hours 

 after copulation (SOBOTTA). The rabbit's egg, like that of the 

 guinea-pig, remains about eighty hours, the dog's egg eight to ten 

 days in the tube (ROTHIG, Embryol. Technik). 



Condition of Ovary as Index to Pregnancy. On opening the body 

 cavity of a mammal, first of all examine the ovary. By so doing 

 one can estimate roughly the time that has elapsed since the dis- 

 charge of the ovum or ova. Prominent stigmata or areas with a 

 blood-shot centre indicate recent ovulation, while a smooth surface 

 of yellowish appearance indicates a corpus luteum, which means 

 that some time has elapsed since ovulation. 



585. Isolation of the Eggs and Early Stages. The tubse and uterus 

 or uteri are dissected out and treated in one of two ways : either 

 the isolated tuba after straightening is washed out from the funnel 

 opening with warm salt solution, or with some fixative like formalin 

 or weak osmic acid, or on the other hand the whole length of the 

 tube is laid open and spread out with a scalpel or sharp scissors and 

 needles, and the eggs are looked for under a dissecting microscope. 



* Eevised by J. B. G. 



