The experiments fully detailed above need little summing-up, since the general result has been appended to each.

The discoveries may be tabulated as follows :-

1. Capillary tubes containing sea-water which has been in contact with ripe eggs of Echinus esculentus soon become plugged with spermatozoa when immersed in a sperm suspension. Control tubes containing normal sea-water, cœlomic fluid, sea-water of different PH and sea-water with immobilising reagents, etc., never contain anything like the same number of sperms as the egg-water tubes.

2. The above result, obtained regularly, is quite contradictory to those of Buller and Loeb on other species of Echinoderms.

3. From the general appearance of the accumulation of sperms, from the fact that a greater length was travelled in the egg-water tubes than in the others, and from the results with capillary tubes containing immobilising reagents, we consider that Echinus esculentus eggs give off substances which actually direct the sperm movements ; in other words, that chemotaxis is demonstrated.

4. The results of Experiments X. and XI. show that in all probability the accumulation of sperms in capillary tubes containing egg-water is due not only to chemotaxis, but also to other phenomena which it is known are produced by egg secretions (aggregation and agglutination of spermatozoa).

5. The chemotactic action of egg-water seems to be specific. Egg-water of similar PH from Echinocardium cordatum had no effect upon sperms of Echinus esculentus.

6. Possibly chemotaxis does not occur in all species of Echinoderms. This might explain the results of Buller and Loeb. It was not demonstrable in Teredo. Moreover, the experiments do not prove that the phenomenon is absolutely necessary for the fertilisation of eggs of Echinus esculentus. On the other hand, they would indicate that chemotaxis does occur in the animal kingdom, and in this respect they support the experiments of Lillie and de Meyer.

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