505 
Protoplasm in Coenocytic Hyphae. 
under less favourable conditions. The microsomes were in 
quite active locomotion through the protoplasm, exhibiting 
a kind of indefinite circulation. Far finer examples of this 
movement were obtained, however, in sowings of Pilobolus 
spores upon the surface of bread-broth. In twelve hours 
after sowing (overnight), they had germinated freely with 
long branching hyphae. Each spore contained a large 
vacuole, and a few small ones appeared in the hyphae. 
The microsomes were especially distinct, and kept up a lively 
coursing in all directions, but more especially lengthwise the 
hyphae and into and out of the spores. They appeared to 
follow no defined routes, which seems to indicate that they 
were not dependent upon circulating currents in the liquid. 
Moreover, sometimes collisions occurred between microsomes 
moving in opposite directions. I have no explanation of this 
phenomenon to offer ; but do not think that it is connected in 
any direct way with the streaming movements in hyphae. It 
was necessary, however, to mention it, in order to distinguish 
it from the floating of microsomes in currents, which I now 
desire to describe. 
I have so far said nothing about return currents in the 
hyphae, but they are occasionally to be seen. When the 
return current exists it is generally well defined, and always 
occupies the periphery of the hyphal cavity. It carries no 
vacuoles, and can only be detected by the movement of the 
microsomes. As the hypha is seen in optical section, there 
appears to be the usual surging, vacuolated stream moving 
through the centre, and on either side next to the walls 
a narrow uniform layer of clear protoplasm, in which minute 
particles are moving in opposite direction to the central 
stream. Between the two streams is a quiescent partition 
of protoplasm of about the same thickness as that lining the 
cell-walls. These quiescent layers vary much in thickness, 
and are at times so thin as to be scarcely discernible. It is 
obvious that whenever such return currents exist, their volume 
is ample to bring back all the protoplasm borne forward by 
the central stream, especially as it has become freed from all 
