ON THE MOVEMENTS OE THE DIATOMACEiE . 899 
surface of Naviculce by means of indigo, and considered bis 
researches corroborative of Nagelks hypothesis. He remarked 
that indigo particles coming in contact with the Diatom re- 
mained quite motionless except along the “ raphe , 33 the line 
of suture : here he observed that the granules were carried 
from the central spot, or “ umbilicus 33 as it is called, slowly 
along to the terminal points of the frustule, where they stopped 
a short time and were then again carried off in a reverse 
direction. He found the currents occasionally so strong that 
bodies of some size were set in motion by them. The Rev. W. 
Smith, in the introduction to his work on British Diatoms, 
states that he is constrained to accept Nagelks hypothesis. 
The fluids (he remarks) which are concerned in these actions must enter 
and he emitted through the minute foramina at the extremities of the 
siliceous valves ; and it may easily be conceived that an exceedingly small 
quantity of water expelled through these minute apertures would be suffi- 
cient to produce movement in bodies of so little specific gravity. 
He concludes, however, by observing that “ the subject is 
one involved in much obscurity, and is probably destined to 
remain, for some time to come, among the mysteries of nature, 
which baffle while they excite inquiry.-” 
We now come to the hypothesis of ee ciliary action.” Ehren- 
berg was the first to start this explanation with singular 
confidence and inconsistency, as we shall see that he had 
already advanced the explanation of a central foot. He gives 
the following minute details, which have only the most remote 
foundation in fact, in reference to Surirella gemma, : — 
Long delicate threads projected where the ribs or transverse markings 
of the shell joined the ribless lateral portions, and which the creature volun- 
tarily drew in or extended. An animalcule, X V of a line long, had twenty- 
four for every two plates, or ninety-six in all. 
These ciliary processes were stated to be actively vibratile, 
while the frustule was declared to be perforated with ninety-six 
apertures for their extrusion. The presence of hair-like pro- 
cesses on all parts of the frustule is not at all unfrequent, and 
it is not improbable that Ehrenberg was deceived by these. 
In plate XVIII. (fig. 4) I have given a drawing of a specimen 
of a living Nitzschia sigmoides , with numerous specimens of 
another Diatom — Amphora minutissima — adhering to it. This 
and similar specimens I observed at Cambridge in June, 1865. 
The Diatom was covered with minute, erect, immovable hair- 
like processes, which were also disposed over the surface of 
the parasitic Ampliorce ; similar hairs were not uncommon on 
other species. There can be little doubt but that these hairs 
are foreign to the Diatom, and are in all probability fungoid 
