ARTIFICIAL PRopUCTION oF NorRMAL Larva 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." 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, 
Thad noright 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- 
1GEMMILL, 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] 
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