2 Transactions of the Society. 
bodies consisting of a firm envelope of cellulose (which is coloured 
purple by chlor-iodide of zinc), containing a greenish-brown endo- 
plasm which at first is very slightly granular, but which draws up 
into isolated particles having a sort of mulberry outline as maturity 
approaches. 
At this stage the cell-wall becomes tumid at one point, and forms 
a process, or beak, which forces its way out between the two shells of 
the diatom, gradually elongates, and then bursts at its extremity. 
Through this beak the contents of the sac are discharged, sometimes 
with great rapidity, into the surrounding water, in the form of a cloud 
of minute zoospores endowed with a great power of rapid motion. 
The beaks or discharging tubes are often of considerable length, say 
half that of the diatom itself. I have never seen more than one beak 
or discharging tube proceeding from any one sac out of the hundreds 
I have had under observation, though Zopf says of his Ectrogella, 
“ I have counted as many as ten, and the fact of many excretory 
ducts being formed in the larger sporangia is particularly characteris- 
tic of Ectrogella. The medium sized usually possess from three to 
five, but sometimes only two.” 
A single Pleurosigma may contain more than one sporange, and 
though one or two is the most common number, eleven have been 
counted in one shell. As a general rule each sac is quite simple, 
but I have observed several somewhat doubtful instances of their 
being bifurcated. Zopf says of the sporanges of his Ectrogella , 
“ They are never branched.” 
1 have not as yet been able to trace the development of the zoo- 
spores after they have left the sac, as they speedily become mixed 
and confounded with the surrounding debris of all sorts accompanying 
the specimens. Though it is easy to separate a sac-bearing specimen 
and isolate it on a clean slide, the necessary manipulation seems to 
completely arrest its powers of further development, and no emission 
of zoospores has taken place in any one instance out of the many 
experiments made. 
Of w 7 hat particular organism these sacs are the zoosporanges can 
only be finally determined by getting their contained zoospores to 
develope under observation, and then tracing the resulting growth 
to its ultimate form. Hitherto, as noted above, 1 have failed to get 
any growth from them under conditions which render accurate observa- 
tion possible, though I have kept the sporanges under constant, or 
rather regular, observation for weeks at a time, while they were 
immersed in plain river water, or in culture fluids in which diatoms 
increase and multiply. Among other culture fluids tried was what 
might be called “diatom soup,” madeby boiling down a large quantity 
of fresh diatoms, and preserving the filtered extract in sterilized and 
sealed tubes. This should give a medium having all the necessary 
elements for the nutrition of these zoospores, whether they be those 
of the diatom itself or of an endophytic parasite. 
