Boar seminal plasma, vesicular secretion and epididymal plasma proteins were studied by gel disc electrophoresis at pH 4\m=.\5and 8\m=.\6and by isoelectric focusing in tubes and on plates using ampholines of pH range 3 to 10.The number of protein bands obtained in the gel disc electrophoresis was fifteen to twenty for all the samples. A similarity between the proteins of the seminal plasma and the vesicular secretion was greater at pH 4\m=.\5than at pH 8\m=.\6.The epididymal plasma showed a different separation picture.The better resolution of the isoelectric focusing revealed a greater number of proteins. Similar protein patterns were found for the vesicular secretion and the seminal plasma in the basic part of the pH range, where the majority of the proteins of these fluids are found. The proteins of the epididymal plasma, on the other hand, possess more neutral isoelectric points and their contribution to the seminal plasma is smaller than that of the vesicular secretion. Only a few of the epididymal plasma proteins and of the minor vesicular secretion proteins could be found in the neutral and acidic regions of the seminal plasma. This is largely the result of the dilution of these accessory secretions occurring during ejaculation.

The EP components were mainly secreted in the first three or four fractions, but occasionally from fraction four onwards. Those of VS were emitted during the entire ejaculation, the maximum occurring in the sperm-rich fraction or the immediately succeeding fraction. The first fractions were devoid of VS components in only one case.The majority of the EP proteins could be identified electrophoretically in the sperm-rich fractions, but the protein patterns in the other fractions were similar to those of VS. The results are discussed and compared with previous findings.

There are few reports in the literature concerning the specific gravity (s.g.) of mammalian spermatozoa and seminal plasma. Lindahl & Kihlstrom (1952) using umbradil salts of methylglucamine as the suspending medium found bull spermatozoa to have a specific gravity of 1\m=.\241to 1\m=.\335.Lindahl & Thunqvist (1965) using Ficoll (polysaccharide of sucrose) obtained values of 1\m=.\21to 1\m=.\33. These results are considerably higher than the specific gravity of 1\m=.\0975 reported by Yamane (1920) for the stallion, and 1\m=.\132reported by Beatty (1964) for the rabbit. They also seem very high in view of the chemical composition of the dry matter and water content as given by Mann (1964) and VanDemark (1948). The specific gravity of bull seminal plasma reported by Anderson (1946) was

There are a few reports on the changes in specific gravity (s.g.) during maturation and ageing of spermatozoa. Lindahl & Kihlstr\l=o"\m (1952) found the s.g. of bull spermatozoa to range between 1\m=.\240and 1\m=.\334.The s.g. decreased from 1\m=.\2867to 1\m=.\2668when three consecutive ejaculates were collected. Lindahl & Thunqvist (1965) found a value of 1\m=.\10to 1\m=.\12for the s.g. of bull epididymal spermatozoa and a value of 1 \m=.\21to 1 \m=.\33 for ejaculated spermatozoa. Assuming that spermatozoa from the epididymis and from later ejaculates are younger than those from the first ejaculates, they suggested that the s.g. of spermatozoa increases with maturation and ageing.Spermatozoa were taken from different parts of the bull testis in order to ascertain whether their s.g. changes during maturation and ageing in the genital tract. Testes were removed immediately after slaughter from twelve healthy bulls, 12 to 14 months old, who had never been allowed to serve a cow. Spermatozoa were collected from the mediastinum testis, caput epididymidis and cauda epididymidis. The sampling was carried out within 2 hr of slaughtering.The determination of the s.g. of spermatozoa was carried out according to the method of Danon & Marikovsky (1964) for determination of the density distribution of a red cell population, which was adopted for determination of density distribution and s.g. of bull spermatozoa by Lavon, Volcani, Amir & Danon (1966).To prevent an alteration in the s.g. of the removed cells, which may be caused by the use of electrolyte solutions, the cells were drawn directly from the organ into capillaries of the type used in micro-haematocrit determinations.The set of capillaries, 32 mm long and 0\ m=. \ 8 mm in diameter, were previously prepared by drawing into each capillary tube a 5 mm column of a non-watermiscible phthalate ester mixture of pre-determined s.g. After sealing in a

Summary. Changes occurring in the proteins of bovine spermatozoa during their migration from the caput to the cauda epididymidis were studied.The percentage of total nitrogen in the dry matter was greater in the cauda than in the caput spermatozoa, but the nitrogen content/109 cells was less in the cauda spermatozoa.