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Summary.

Melanizing activity of semen varied between males and between ejaculates of the same male. Samples of semen with yellow colour showed stronger melanizing activity than other samples. The percentage of live spermatozoa found after different levels of temperature shock was uniformly less in semen with strong melanizing activity than in semen with weak melanizing activity. The observed variation in live spermatozoa after shock treatments followed a curvilinear trend with slopes varying among the species studied.

Summary.

Exposure of male mice to a 1·8/1·0 mixture of air/CO₂ for a total of 6 hr reduced the area and breadth of the head and of the midpiece of live spermatozoa in the vasa deferentia. During a total of 26½ hr exposure spread over 6 days, males when test-mated had a low conception rate but the numbers of offspring in the litters produced were normal. The low conception rate of males appeared to persist even 15 days after the end of treatment.

Summary.

Dimensional characteristics and proportions of live spermatozoa in permanent nigrosin—eosin preparations from the semen samples of Murrah buffalo bulls were studied in different seasons. Between bulls, all the characteristics varied significantly. Between seasons, all the characteristics, except length of head and mid-piece, varied significantly. Environmental temperature and humidity both appeared to influence the dimensional and enumeration characteristics of the spermatozoa. The percentage of live spermatozoa decreased with increase in air temperature and humidity.

Melanizing activity of rabbit semen was reported by Beatty (1956). The activity—colour reaction when semen is supplied with dihydroxyphenylalanine—varied between males with different pelt colours : black rabbits showed intense melanizing activity and albinos none. It was further observed that the pale colour of semen was a characteristic of dark pelted bucks, and that the colour of the semen was, in some way, related to its melanizing activity. Mukherjee (1964) studied the melanizing activity of the semen of bulls, goats and rams, and observed that the activity varied between animals and between ejaculates from the same animal. Although there was no appreciable relationship between the coat colour of these animals and the melanizing activity of the semen, the yellow semen samples showed stronger melanizing activity than the non-yellow ones. The proportion of 'live' (unstained in eosin-nigrosin) spermatozoa was uniformly less in strongly melanizing semen samples than in weakly melanizing

Summary.

The mid-piece of fully matured mouse spermatozoa showed differential dehydrogenase activity. With the decreased activity, the breadth and area of the mid-piece decreased. Injection of 0·06 mg of adrenaline/male decreased the percentage of spermatozoa with high dehydrogenase activity.

Summary.

In inbred male mice sampled at a standard time of year, increased age was accompanied by a marked fall in the proportion of spermatozoa with normal acrosomal caps, thus indicating a concomitant fall in fertility. Age trends were noted in the projected area of the midpiece and perhaps also in the breadth of the spermatozoan head. There was no significant age trend in the projected area of the spermatozoan head or the length of the midpiece. No difference of any kind was detected between the spermatozoa of albino and heterozygous albino males.