3. The fact has been mentioned that the most motile sperm will not be able to enter into the egg if certain other conditions (specificity or COH or CCa) are not fulfilled. On the other hand, living but immobile sperm cannot enter the egg under any conditions. If we add a trace of KCN to the sperm of Arbacia so that the spermatozoön becomes immobile no egg is fertilized even if the eggs and the sperm are thoroughly shaken together; while the same spermatozoa will fertilize these eggs as soon as the HCN has evaporated and they again become motile. It was formerly thought that the spermatozoön had to bore itself into the egg, being propelled by the movements of the flagellum. It is, however, more probable that only a certain energy of vibration is needed on the part of the spermatozoön to make the latter stick to the surface of the egg and agglutinate and that later forces of a different character bring the spermatozoön into the egg. The fact that under normal conditions a very slight degree of motility on the part of the spermatozoön allows it to enter the egg of its own species seems to favour such a view.
It is a common experience that spermatozoa become very active when they reach the neighbourhood of an egg. v. Dungern assumed that only foreign sperm became thus active, but F. R. Lillie[69] has pointed out that this may be a specific effect. The writer tested this idea on the sperm and eggs of two species of starfish and of sea urchins. It should be mentioned that the eggs of the starfish used in this experiment were completely immature and could not be fertilized, while the eggs of the sea urchins were mature. The testicles and ovaries had been kept in NaCl and all the sperm was immotile. Eggs and sperm were mixed together in a pure m/2 NaCl solution where the sperm was only rendered motile by the proximity of eggs. The following table gives the result.[70]
TABLE V
Specificity of Activation of Sperm by Eggs
| Asterias♂ | Asterina♂ | Franciscanus♂ | Purpuratus♂ | |
|---|---|---|---|---|
| Asterias♀ (immature) | Immediately very motile. | No activation. | Moderately active. | Slight effect in immediate contact with egg. |
| Asterina♀ (immature) | Not motile. | Violent activity. | Violent activity. | Slight effect only near the egg. |
| Franciscanus♀ (mature) | Slightly motile. | No motility. | Immediately active. | Immediately active. |
| Purpuratus♀ (mature) | Slightly motile after some time. | Slight effect in immediate contact with eggs. | Immediately active. | Immediately active. |
The spermatozoa of starfish show a marked specificity inasmuch as they are strongly activated only by the eggs of their own species, although in this experiment these were immature, and to a slight degree only by the eggs of the sea urchin purpuratus. But it is also obvious that the specificity is far from exclusive since the immature eggs of Asterina activate the sperm of the sea urchin franciscanus as powerfully as is done by the mature eggs of the sea urchin purpuratus and franciscanus. In studying these results the reader must keep in mind first that all these experiments were made in a NaCl solution and second that it requires a stronger influence to activate the spermatozoa of the starfish, which are not motile at first even in sea water, than the sea urchin spermatozoa which are from the first very active in such sea water, and which may therefore be considered as being at the threshold of activity in pure NaCl solution.
Wasteneys and the writer (in experiments not yet published) did not succeed in demonstrating an activating effect of the eggs of various marine teleosts upon sperm of the same species.
4. F. R. Lillie[71] has studied the very striking phenomenon of transitory sperm agglutination which takes place when the sperm of a sea urchin or of certain annelids is put into the supernatant sea water of eggs of the same species. If we put one or more drops of a very thick sperm suspension of the Californian sea urchin S. purpuratus carefully into the centre of a dish containing 3 c.c. of ordinary sea water and let the drop stand for one-half to one minute and then by gentle agitation mix the sperm with the sea water the mass of thick sperm which is at first rather viscous is distributed equally in sea water in a few seconds and the result is a homogeneous sperm suspension. When, however, the same experiment is made with the sea water which has been standing for a short time over a large mass of eggs of the same species, the thick drop of sperm seems to be less miscible and instead of a homogeneous suspension we get, as a result, the formation of a large number of distinct clusters which are visible to the naked eye and which may possess a diameter of 1 or 2 mm. The rest of the sea water is almost free from sperm. These clusters of spermatozoa may last for from two to ten minutes and then dissolve by the gradual detachment of the spermatozoa from the periphery of the cluster.
This phenomenon seems to occur in sea urchins and annelids. The writer has vainly looked for it in different forms of the Californian starfish or molluscs and in fish at Woods Hole. Lillie failed to find it in the starfish at Woods Hole.
The writer found that the sperm of the Californian sea urchin Strongylocentrotus purpuratus will form clusters with the egg sea water of purpuratus but not with that of franciscanus; while the sperm of franciscanus will agglutinate with the egg sea water of both species, but the clusters last a little longer with the eggs of its own species.