Forty-three males were divided into three experimental groups and ligatures placed unilaterally as follows: (1) on the ductus deferens, (2) on the ductus deferens and corpus epididymidis, and (3) on the ductus deferens, corpus epididymidis and ductuli efferentes. Semen was collected six times a week from all males before ligation and for as long as 12 weeks thereafter. Spermatozoa transported normally from the caput to the cauda epididymidis in non-ligated controls were characterized by rapid

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... gration of the protoplasmic droplets, a decrease in swollen acrosomes and other abnormalities, an increase in the percentage of motile cells and a striking increase in fertility. Ligation of the ductus deferens only had little effect upon any of these changes. Also, considerable motility and fertility was maintained for 12 weeks following single ligation in contrast to a reduction after 4 weeks in the group with the isolated cauda epididymidis. This suggests that considerable mixing of spermatozoa normally can occur in the cauda. The proportion of abnormal forms, particularly decapitated spermatozoa, increased considerably in the isolated cauda by 8 weeks. In the isolated caput abnormal spermatozoa increased rapidly and motility decreased. The protoplasmic droplet movement was delayed, as 54% had droplets on the midpiece after 4 weeks in contrast with 16% on spermatozoa which migrated normally to the cauda. Severe degeneration and disappearance of spermatozoa followed after 4 weeks, indicating that the caput may have dissolution properties. Litter size, based on all does inseminated, averaged only 0\m=.\5for caput spermatozoa compared with 5\m=.\0for both caudal and ejaculated spermatozoa. The morphological and fertility data indicate that extrinsic factors as well as intrinsic ones are required for complete development of the fertilizing capacity of rabbit spermatozoa.