520 FRANK R. LILLIE 



in vessels of varying form, et cetera; under certain conditions the 

 aggregations may arise in conformity wijbh the water currents set 

 up by the last emptying of the pipette, et cetera. But a descrip- 

 tion of these variations would be useless without the analysis of 

 the causes of the phenomenon, which is taken up later. 



All the experiments on Nereis to be described beyond were made 

 with aggregative sperm, so that there was always a test, which had 

 the advantage of being macroscopic and quick, of the activity of 

 the sperm used in the experiments, and this has much to do with 

 uniformity of results. 



To give a more concrete idea I reproduce three photographs, 

 natural size, of the phenomenon of aggregation. The first (fig. 1) 

 was taken ninety seconds after mixing a drop of dry sperm in 

 about 8 cc. of sea-water. The aggregations are quite uniformly 

 distributed except in the upper right quarter where their arrange- 

 ment marks out original currents produced by mixing with the 

 pipette. Figure 2 was likewise taken ninety seconds after 

 mixing; the effect of water currents on the arrangement of the 

 aggregations is shown here quite well on the left. Figure 3 was 

 taken three minutes after mixing, and the separate aggregations 

 are beginning to fuse together on the bottom. 



I propose to discuss in this section simply the conditions which 

 modify the activity of the spermatozoa. In the case of Nereis 

 such conditions may be inferred from two kinds of observations, 

 namely : (1) The appearance of activity presented to the eye under 

 the microscope and (2) the rate and degree of the aggregation reac- 

 tion which is macroscopic. Nereis is the only form with which I 

 am familiar that exhibits the latter reaction in any marked way. 

 Its sperm is therefore better adapted than that of any other species 

 for study of conditions of activity. The observations of different 

 samples of sperm under the microscope are very difficult to com- 

 pare as to degree of activity, as one is never sure of the successive 

 subjective impressions, but in the case of Nereis these can be 

 checked by the aggregation reaction. 



The principle conditions that affect activity are 'freshness,' 

 temperature, and the chemical constitution of the medium. 

 These conditions will be considered not exhaustively at all, but 



