A method of obtaining samples of semen from rabbit males by means of a dummy and artificial vagina is described. The volume of the semen, and the number of spermatozoa per cm. (density) and the total number of spermatozoa in the sample have been measured. The data obtained from these measurements have been analysed under the following headings:

1. Relation between total volume and total number of spermatozoa. With an increase in the total volume of the ejaculate there is an increase in the total number of spermatozoa, but the relationship is not linear. The density of spermatozoa varies considerably.

2. Seasonal variation. Seasonal variation in sperm production is not marked in these data. There is slight tendency for the numbers to be highest in the early part of the year and lowest in August and September when the animal is moulting.

3. Individual variation. In each individual, variation is considerable. Differences between individuals are not marked, but as most of the animals were of low average fertility, it is probable that this result is not typical of male rabbits in general.

4. Effect of successive matings with in a short period. In successive matings the number of spermatozoa diminishes rapidly. As the density is not much affected, the diminution is due to reduction in the volume of the ejaculate.

5. Relation between the number of spermatozoa in the ejaculate and the number in the various sections of the spermatic tract. After a series of samples had been obtained, some males were killed and an estimate made of the number of spermatozoa present in various parts of the tract. From the results it is concluded that on ejaculation the vas deferens is practically emptied and that some sperm in the ejaculate come from the cauda epididymis.

6. Observations on sexual behaviour. The sexual pattern of the male rabbit is described and the relation between sexual stimulation and sex drive is discussed.