C. R. AUSTIN AND M. W. H. BISHOP 77 



in the incidence of abnormal fertilization in rats ( Blandau, 1952 ) 

 and rabbits (Chang, 1952b) and of polyspermic fertilization in 

 rats and rabbits ( Austin and Braden, 1953a,b ) and mice ( Braden 

 and Austin, 1954b), an increase in the incidence of abnormal 

 pregnancy, and reduction in the number of normal young born 

 in the guinea pig ( Blandau and Young, 1939 ) , rat ( Soderwall and 

 Blandau, 1941; Blandau and Jordan, 1941), rabbit (Hammond, 

 1934), sheep (Quinlan, Mare, and Roux, 1932), sow (Lewis, 

 1911), and cow (Trimberger, 1948). 



Both mechanical and physical attributes of the female genital 

 tract also reduce greatly the numbers of spermatozoa passing to 

 the site of fertilization (Braden, 1953). The chief agents in this 

 process of reduction are the cei^vix (in species having intravagi- 

 nal ejaculation), utero-tubal junction, and tubal isthmus by vir- 

 tue of their narrow lumen, and the uterus, by virtue of its large 

 internal surface area (rabbit) or voluminous fluid content (ro- 

 dents especially ) . Leonard and Perlman ( 1949 ) found that, in 

 the rat, only vigorously motile spermatozoa could pass the utero- 

 tubal junction. Furthermore, not only were inert particles and 

 immotile spermatozoa unable to pass the junction, but active 

 spermatozoa of other species (bull, mouse, and guinea pig) were 

 similarly unable to enter the Fallopian tube, even when mixed 

 with active rat spermatozoa. By contrast, in the cow, dead sper- 

 matozoa were transported as rapidly as living ones (Van Demark 

 and Moeller, 1951 ) , and rat spermatozoa were found to be capa- 

 ble of passing into the Fallopian tube of the ewe (Phillips and 

 Andrews, 1937). Consistently, the pressure required to force flu- 

 ids from the uterus to the tubes is very high in the rat (Alden, 

 1943) and low in the sheep and cow (Andersen, 1928). Ander- 

 sen's paper contains descriptions of the morphology of the utero- 

 tubal junction in 25 mammals belonging to 10 different orders, 

 which indicate that the restrictive power of the region must differ 

 widely among these species. She noted, too, that fluid could not 

 be forced from the uterus to the tube in the cat and rabbit, and 

 that passage was difficult in the sow at the time when eggs are 

 in the tubes. The comparative freedom of passage through the 

 utero-tubal junction of the cow is illustrated by Rowson's (1955) 



