546 FRANK R. LILLIE 



availa])lo filter paper o-ive a distinct acid test, iisin^ tlie spermato- 

 zoa of Nen^is as indicator: A drop injected into a fresh sperm sus- 

 p(Mision in\'ariably gave the ring formation with outer clear l)order, 

 which is the characteristic and unmistakable acid reaction. This 

 suggests the possible use of such cells as indicators in certain 

 classes of experiments; some preliminary observations whicli 1 

 have made concerning CO., production of dividing eggs by this 

 method are distinctly promising, though the results are compli- 

 cated by the usual presence of other substances. 



9. Chemotnxis to egg-secretions 



The spermatozoa of Nereis exhibit positive chemotaxis to egg- 

 secretions, which may be demonstrated in the same way as the 

 l)ositive chemotaxis to acids, l)ut this subject, which is of course 

 the most important i)art with reference to the fertilization 

 problem, may be postponed to the next section dealing with 

 agglutination phenomena, because it is always associated with 

 agglutination. 



B. ARBACIA 



The reactions of Arbacia spermatozoa are essentially the same 

 in principle as those of Nereis, but on account of the lesser sensi- 

 tiveness of the spermatozoa, as noted in the section on activation 

 phenomena, the reactions are much slower and less clearly defined. 

 This may be illustrated by the notes on a single experiment : 

 July 20, 1912. A fresh suspension of Arbacia sperm was made by 

 mixing two drops of the dry si:)erm with 9 cc. of sea-water. The 

 suspension appears milky, and the spermatozoa are decidedly 

 active under the microscope. A portion was immediately moun- 

 ted under a raised cover-slip and two drops of 5 per cent COo 

 sea-water were injected some distance apart. At first there 

 appeared to be no reaction, as contrasted with Nereis in which 

 I'ing formation is almost instantaneous under such circumstances. 

 In two minutes the sites of the drops became more cloudy than 

 the rest of the slide, and a faintly defined clear margin began to 

 appear surrounding the drop. The jiicture gradually gained in 

 definiteness until it became very clear. The central aggrega- 



