Physiology of the Spermatozoa of .Ferns, 577 
The detrimental effect of distilled water upon the life of 
spermatozoa has already been remarked by Pfeffer h In my 
experiments with hanging drops of distilled water it was 
found that the majority of spermatozoa came to rest in about 
thirty minutes, the longest time of movement being just one 
hour. The swarm-period was thus reduced to less than one- 
third of that obtained with tap-water. The distilled 2 water 
was not shaken up before use. I was under the impression 
that the shallow hanging drops exposed to the air in the 
glass-cells would almost immediately become saturated with 
oxygen. From the work of Senn 3 , with which I have since 
become acquainted, this appears to have been a mistake. 
Senn found that in hanging drops of distilled water which 
had not been shaken up with air Coelastrum reticulatum 
formed colonies or coenobia. In similar drops of distilled 
water which had been previously shaken up with air the Alga 
gave rise to single unconnected cells. The difference in the 
behaviour of the Alga in the two cases is due to the different 
amount of oxygen in the drops. Similarly the difference in 
the amount of oxygen in hanging drops of tap-water and of 
distilled water may determine the difference in the swarm- 
period of spermatozoa in the two cases. 
Pfeffer 4 found that spermatozoa swarmed at least twice as 
long in an open drop of water as in an ordinary coverglass- 
preparation where the coverglass was supported by strips of 
paper, and at least five times as long as in an ordinary pre¬ 
paration not so supported. He attributed the differences in the 
length of the swarm-periods to the amount of oxygen present 
in the different cases. It is to be regretted that neither 
Strasburger nor Voegler have stated the exact methods which 
they employed in determining swarm-periods. If coverglass- 
preparations, which indeed Voegler 5 appears to have used, 
or hanging drops made with unshaken distilled water were 
1 Pfeffer, loc. cit, Bd. i, p. 368, Anm. 3. 
2 Doubly distilled and put in a specially cleaned two-litre flask. 
3 Senn, Ueber einige coloniebildende einzellige Algen. Dissertation, Basel, 1899, 
p. 13. 
4 Pfeffer, loc. cit., Bd. i, p. 372. 5 Voegler, loc. cit., p. 646. 
Q q 2 
