ARTIFICIAL PRODUCTION OF NORMAL LARV.E 597 



contain spermatozoa. It is imperative to guard against 

 both possibilities. The sea-urchins have practically died 

 out in the immediate neighborhood of the Woods Hole 

 laboratory, and we have to send out the steam launch to 

 collect them. For this reason even at the height of the 

 spawning reason there is little danger of the sea-water con- 

 taining spermatozoa in such quantities as to interfere with 

 experiments on unfertilized eggs. Moreover the danger that 

 the spermatozoa contained in the sea-water of the laboratory 

 may interfere with experiments on unfertilized eggs is not 

 very great, even at the height of the breeding season. This 

 is shown indirectly by the fact that in the experiments 

 described in the previous chapter not a single egg was fer- 

 tilized through contamination of the sea-water with sper- 

 matozoa. The spermatozoa if scattered in sea- water soon lose 

 the power of impregnating the egg. Gemmill found experi- 

 mentally that this occurs in less than five hours after the 

 spermatozoa leave the testicle. 1 My experiments were carried 

 on after the breeding season was practically over, in Septem- 

 ber, when the majority of sea-urchins contained practically 

 no more eggs. I had already made up my mind that my 

 further experiments would have to be postponed a year, when 

 through the kindness of Professor Bumpus of the Fish Com- 

 mission I obtained a few dozen sea-urchins that he had col- 

 lected early in the season and kept in a small pond. It 

 happened that almost every one of these animals was a female 

 and full of eggs. Though there was little possibility that the 

 running water of the marine laboratory could contain any 

 spermatozoa of sea-urchins which were able to fertilize eggs, 

 I had no right to take anything for granted in this direction. 

 I therefore conducted with each experiment a series of con- 

 trol experiments to guard against the possibility of contam- 



1 GEMMILL, Journal of Anatomy and Physiology, Vol. XXIV (1900), p. 163. The 

 results are much better if sterile sea-water is used, as was the case in Fischer's ex- 

 periments. [1903] 



