94 MR. Н. М. WARD ON THE STRUCTURE, DEVELOPMENT, 
clearness in a fortunate vertical section passing radially through an arm of the latter. 
Under certain conditions very many of the cells become thus modified. 
After the protoplasmic contents (in which are contained much coloured fatty and starchy 
matter) have become transformed into the young zoospores *, some time frequently elapses 
before further changes occur. If a thallus in the condition of fig. 16 be allowed to 
remain tolerably dry for a day or two, and be then moistened with water under the micro- 
scope, the sacs may be observed to burst one after another in somewhat rapid suc- 
cession, each emitting numerous actively moving zoospores from a perforation in the 
apex. ‘This perforation is at first sight somewhat complex: the wall of the sac itself 
presents a slight papilla with a round opening or pore; but above this is frequently seen 
an irregular, usually long slit, through a thin homogeneous membrane on the exterior ; 
this membrane is a cuticular one, apparently proper to the thallus, and seen in vertical 
sections (figs. 8 & 12) from an early date. Itis not an uncommon event to see several of 
the zoospores remain behind, and move about actively for some time in the otherwise 
empty sac (fig. 43). 
The zoospores emitted by this sac t are remarkable bodies in several respects : each passes 
out as a delicate fusiform body, measuring about сууу to обо in. long, with granular 
contents, and a distinct orange tint, due apparently to small granules of the same nature 
as the oily globules &c. in the thallus-cells. Its motion is at first very rapid, with a con- 
stant tendency to jerks; and one cilium is trailed laterally, while the other moves actively 
in front (РІ. ХХІ. fig. 47). In a minute or so the jerking motion is replaced by an even 
gliding, the zoospore swimming round and round in circles, both cilia being now usually 
active. This movement soon becomes slower, and as it does so the fusiform shape 
becomes exchanged for a spherical one, until, usually within three minutes or so, the 
zoospore comes to rest as a perfect sphere, with two slowly waving flagella at one pole. 
Within the next two minutes or so the feebly waving ends of the flagella come to rest, 
coiling themselves irregularly, or forming two circular loops (fig. 47), with the ends 
approximated or united. Many of the spheres now absorb water, swell up like hollow 
vesicles, and burst irregularly, scattering the small oval granules, which dance about 
with active Brownian motion. The above sequence of processes is not described for one 
case only ; І have observed it many times. In some cases there have been more than а 
hundred of the sacs bursting at once; and each emitting many zoospores, certainly more 
than thirty or forty. 
. . One of the sacs, measured just before bursting, was about 44155 in. long by то broad ; 
and the spherical zoospores, just come to rest, measure, on an average, about кус to sooo 
in. in diameter. The very small pale oval granules found in the zoospore, and set free 
when it bursts, average, as near as I can measure, about ;5555 in. long. These bodies 
are often seen moving in the zoospore, and tend to become arranged at the periphery 
* This term is here used provisionally; no proof exists of the exact nature of these bodies, as in the case of the 
zoospore derived from the “ fertile hairs.” 
+ I have purposely avoided suggesting a name for the sac and its contents, since the functions of the zoospores are 
not yet clear. 
