214 Barrett . — Development and Sexuality of some 
species. This condition is more clearly brought out in zoospores killed 
with osmic acid. 
There seems to be considerable variation among the species of this and 
other related genera in the position and number of the cilia on the zoospores. 
Cornu (6) observed in all species studied by him but one cilium. A. Fischer 
(12) found in the case of Olpidiopsis (Pseudolpidium), Rozella , and Woronina 
that the zoospores possessed two cilia, one placed in front and extending to 
the fore, the other attached laterally and extending to the rear. This same 
relation of the cilia was later (13) observed by him for the zoospores of his 
O . Saprolegniae , and was considered to be the normal condition for the 
genus. 
Butler (4) records some interesting observations in reference to this 
point. He found the arrangement of the cilia as described by Fischer 
to exist in Olpidiopsis minor , A. Fischer ; Pseudolpidinm (? Olpidiopsis) 
Saprolegniae , (A. Br.) A. Fischer ; P. gracile , Butler ; and Pleolpidium 
inflatum , Butler. It is interesting to note that in the last-named species, 
he observed what appeared to be a variation in the position of the cilia. 
This he attributed to the varying position of the zoospore in swimming. In 
Pseudolpidium Aphanomyces, (Cornu) A. Fischer, and in Pleolpidium Pythii, 
Butler, the cilia are attached laterally and at the same point. 
It is difficult, in many cases, to observe the attachment of the cilia on 
the living zoospore. However, this can be done without difficulty with the 
proper apparatus. Zoospores were allowed to escape from the sporangium 
into a small hanging drop of water in a Van Tieghem cell, and there 
observed with a 2 mm. Zeiss apo. obj. by the aid of strong artificial light. 
As the zoospores come to rest the attachment of the cilia was clearly 
seen to be at the same point. As has been frequently observed in other 
species, one cilium of the zoospore in motion trails behind. My obser- 
vations revealed that this rear cilium crosses at an angle the upper end 
of the zoospore, and leaving it usually at the side gives it the appear- 
ance of being attached at that point. It was not until a number of ob- 
servations were made that this peculiar condition was detected. When 
once seen it was easily verified for all the species of Olpidiopsis 
studied. 
The same condition was found on careful examination in stained 
preparations of zoospores. In cases where the stain was not too deep, the 
rear cilium could be followed crossing the upper end of the zoospore to 
its point of attachment near that of the other. Occasionally both cilia 
extend out free from the body of the zoospore and leave no doubt what- 
ever as to their relative position. In cases which present the appearance 
of a lateral attachment for one of the cilia, this cilium appears to be shorter 
than the other, but is actually about the same length (see PI. XXIII, Figs, i, 
2, and 15). A more careful examination of the zoospores of other species 
