ABSTRACT
Egg-secretions increase the rate at which the spermatozoa of E. esculentus absorb oxygen by about 300 per cent. Similar secretions may exert little or no effect on the respiratory level of the spermatozoa of E. miliaris. This difference between the species corresponds to the difference visible in the effect of the secretions on the mechanical activity of the two types of sperm.
In the presence of egg-secretions the respiratory activity remains constant at a high level for at least 1 hour, whereas in the absence of secretions the level falls to about 30 per cent, of its original value in the same period of time. This effect is observed in both E. esculentus and E. miliaris.
It is well known that the secretions given off by ripe unfertilised eggs have a marked activating effect upon the mechanical movements of spermatozoa. When the ripe spermatozoa of Echinus esculentus are shed into normal sea-water they become active, but the intensity of their movements is greatly increased by the presence of egg-secretions ; that this effect of egg-secretions is clearly reflected in the change of respiratory level of the suspension is shown by Table I. In the case of E. miliaris on the other hand, the spermatozoa are normally very active in seawater, and the visible increase in activity produced by egg-secretions may be negligible. This also is illustrated in Table I.
The sperm of E. esculentus is often relatively inactive until exposed to egg-secretions ; the sperm of E. miliaris, on the other hand, is usually very active in pure sea-water. Individual males differ considerably in these respects.
It has been shown in a previous paper (Gray 1928) that the activity of a sperm suspension in pure sea-water declines from the beginning of active life, and one of the most remarkable effects produced by egg-secretions is that they delay this process of decline for a significant period of time. Fig. 1 and Tables II and III show that after one hour of active life in sea-water, the respiratory activity of a suspension falls to about 30 per cent, of its original value, whereas a corresponding suspension in sea-water containing egg-secretions still retains about 90 per cent, of its original activity.
Graph illustrating the effect of egg-secretions on oxygen consumption of E.miliaris sperm. The unbroken line shows the oxygen consumed by a suspension in the presence of egg-secretions ; the broken line shows the oxygen consumption of an identical suspension without egg-secretions.
This effect of egg-secretions might be interpreted to mean that these substances exert a specific action on the metabolic processes of the motile spermatozoa in that they definitely inhibit senescence. It should be noted, however, that even in the presence of abundant egg-secretions senescence sets in after about 1½ hours (see Fig. 2).
Graph illustrating the fall of respiratory activity of E. miliaris sperm in the presence of egg-secretions. Note that the rate of oxygen consumption falls rapidly after about 2 hours of active life.
The significance of egg-secretions during the actual process of fertilisation has been discussed by F.R. Lillie (1915), but the experiments here described indicate that their effect is exerted, at least in part, on the spermatozoa rather than on the egg.
By increasing the mechanical activity of the sperm, the secretions must tend to increase its fertilising capacity by reducing the time required to reach and enter a fertilisable egg. If the mechanical activity is accurately reflected by the rate of oxygen consumption, then when spermatozoa are shed into water containing ripe unfertilised eggs their fertilising capacity should be maintained at a maximum value for at least 1 hour. Whereas if eggs are not present it should begin to fall almost from the first moments of activity.
