H. M. FucHS -273 



had lain in it befbi'e being fertilized. Ill was made to show the effect 

 of extract on the sperm, for comparison. 



The Table shows that in both parts of the experiment — with the 

 stronger sperm and with the weaker sperm — the pei'centages in II were 

 1 °/„ higher than those in I. This fact may be due to one of three 

 causes. It may be experimental error ; but the fact that the difference 

 is the same in both parts of the experiment argues against this. Again, 

 it may be that the eggs (b) were affected by their stay in the extract 

 previous to fertilization, so that they became more easily fertilizable — 

 although to a very slight extent. Lastly, the increase may have been 

 due to the action of the 1 cc. of extract introduced with the eggs (b) 

 on the sperm, at the moment of fertilization. A comparison of these 

 figures with those in III, which shows the very large increase in the 

 fertilizing power of the sperm caused by a previous treatment with 

 extract of the full strength, shows that the last of the three possible 

 explanations given above is almost certainly the correct one. 



Thus from the experiments recorded in Tables IX, X and XI, we 

 can draw the conclusion that the excess in the number of eggs fertilized 

 by a given amount of sperm in the presence of extract over the number 

 fertilized in jjlain water is due to an action of the extract on the sperm 

 and not on the eggs. 



3. Effect of egg-extract on the fertilizing pmoer nf the upervf of 

 Strongylocentrotus. 



The experiments already recorded on the influence of egg- and 

 ovary-extracts on the proportion of eggs fertilized by a given con- 

 centration of sperm-suspension have, with one exception, all been 

 made with Ciona intestinalis. In the following section, experiments 

 are described on the effect of egg-extract on the fertilizing power of 

 the spermatozoa of Strongylocentrotus liviclus. 



The first experiment is a plain comparison of the effects of fertilizing 

 with sperm-suspensions of equal concentration, made up in (1) plain 

 sea- water, and (2) egg-extract. The experiment was made for four 

 different strengths of sperm. 



A sperm-suspension was made up, and a given number of drops, 

 added to (1) 10 cc. sea-water, (2) 10 cc. extract. Each of these were 

 then poured on to approximately equal numbers of eggs. 



The Table shows that the extract had the same effect on the per- 

 centages of eggs fertilized as was the case with Ciona and Ascidia. 



If equal amounts of the same sperm-suspension be added to equal 



Jouni, of Gen, jv 18 



