552 FRANK -R. LILLIE 



when a drop of sea-water so charged is injected into a fresh sperm 

 suspension beneath a raised cover shp. The activation is not 

 so pronounced in this case as in Arbacia. The aggregation phe- 

 nomenon is the same. The agglutinations are substantially 

 permanent in Nereis; the spermatozoa stick together much more 

 firmly. 



In what follows we may leave the activation and aggregation 

 phenomena out of account for the most part and confine ourselves 

 to the problems of agglutination. The substance which causes 

 agglutination of the spermatozoa we shall call the sperm agglu- 

 tinin. The agglutination may be shown very strikingly in a 

 vial of fresh sperm suspension. In the case of Arbacia the 

 addition of two or three drops of egg sea-water 1 /4, which has stood 

 half-an-hour, to about 2 cc. of a fresh milkj^ sperm suspension 

 causes formation of agglutinations 1 to 2 mm. in diameter in a 

 few seconds. The agglutination may be so • strong that the 

 fluid between the white agglutinated masses appears perfectly 

 clear. The masses gradually fade from view in a few minutes, 

 but microscopic agglutinations may remain half-an-hour or 

 more. 



The degree of agglutination is of course dependent on the den- 

 sity of the suspension. This is shown by the following experi- 

 ment : Ovaries and eggs of Arbacia were cut up in about four times 

 th.eir own bulk of sea-water and allowed to settle. Two cubic 

 centimeters of the supernatant fluid was put in each of three vials. 

 To one was added 3 drops of a fresh milky sperm suspension, to 

 the next 12 drops of the same, to the third 36 drops. No visible 

 agglutinations formed in the first; in the second agglutinations 

 became visible to the naked eye almost immediately, in the third 

 agglutinations were larger, more numerous, and apparently more 

 solid. 



3. OVA ALONE PRODUCE THE AGGLUTINATING SUBSTANCE 



The eggs of both forms thus produce an agglutinin in the sea- 

 water. The next question is whether the agglutinin is specifically 

 an egg-product. A considerable number of experiments prove 

 that this is the case. The large body cavity of Arbaci^is filled 

 with abundant coelomic fluid and this may be supposed to 



