126 WILLIAM B. KIRKHAM 



The mouse ovum leaves the ovary with a supply of food ma- 

 terial sufficient, with what serous fluid is available for absorp- 

 tion in the fallopian tube and uterine cavity, to maintain its 

 metabolism during fertilization and subsequent cleavage, through 

 the formation of a blastula. These various processes appear 

 to involve very stable mechanisms, for although in mice of all 

 colors a small number of eggs are eliminated immediately after 

 ovulation through inability, or accidental failure, to unite with 

 sperm cells, eggs which have been fertihzed and yet are so patho- 

 logical as to have had development brought to a standstill be- 

 tween the stages of fertilization and implantation are very rarely 

 seen. Implantation, on the other hand, evidently involves a 

 much less stable set of factors than does cleavage, since in white 

 mice counts of thirty-four sets of cleaving ova and of blastulas 

 average more than seven individuals to the set, while thirty- 

 three Utters of new-born young obtained during the same period 

 from mice living under identical conditions and of the same 

 stock averaged less than five; Further evidence for the above 

 statement is the fact that the writer's stock has never yielded 

 a litter of more than nine young, while one set of ten cleaving 

 eggs, another of thirteen, and a set of eleven blastulas have been 

 found, and, as will be again stated later, in mice other than 

 yellow, degeneration of embryos after implantation is rare, and 

 when it occurs is due in most, if not all instances, to infection. 



Many unsolved problems remain in connection with implanta- 

 tion, but there exists now sufficient evidence to render certain 

 the existence of two distinct sets of factors, one maternal, the 

 other embryonic. The work of Fraenkel and Cohn ('10), Loeb 

 ('08), Marshall and Jolly ('10), and others has shown that the 

 corpora lutea are responsible for a stimulus which causes the 

 uterine mucosa to proliferate, a necessary process antecedent 

 to the implantation of the blastulas. Adler ('12) and the writer 

 (Kirkham,'18) have also proved that when lactation is in prog- 

 ress the mammary glands exert some sort of inhibitory in- 

 fluence upon both the stimuli reaching the uterine mucosa from 

 the corpora lutea and those coming from the blastulas. The 

 stunulus from the mouse blastula causes first a further swelling 



