404 
POPULAE SCIENCE EEVIEW. 
that the external movements are referrible to the movement 
of this protoplasm.” Unfortunately, however, as it may seem. 
Professor Schultze could not see this protoplasm ; for although 
he had clearly witnessed the movement of granular protoplasm 
along the raphe in the interior of the frustule, in no Diatom 
could he observe it externally. When we reflect upon the 
very great difficulties offered by the minuteness of the diatom, 
the refraction of the siliceous shell, and the close packing of 
the endochrome, we cannot but admire very highly the per- 
severance and acumen displayed by Professor Schultze. 
Having satisfied himself that no external movement of 
granular protoplasm could be detected, after examining 
Pleurosigma, Surirella , and many others, our observer came 
to the only conclusion open to him — and that was, that the 
protoplasm moving on the exterior of the raphe is hyaline, 
and totally free from granules, just as are the pseudopodia of 
Gromia and Difflugia , described by him. The minute per- 
forations in the shell along the raphe (alluded to above) are 
so very minute as to be scarcely appreciable with the micro- 
scope, and it is through these holes that the protoplasm has 
to flow. Accordingly, its granules, or those of any visible 
size, are of necessity kept back within the frustule, whilst the 
clear hyaline matter flows slowly over the exterior of the 
raphe — moving with the inner protoplasm, whose flow is more 
obvious from the presence of the granules suspended in it. 
Hence the band of protoplasm coating the raphe has the 
import of a foot, on which the Diatom creeps, and there can 
be little doubt that Professor Schultze has set the long- 
debated question of these movements at rest. I should wish 
here to point out how very near Mr. Wenhands observations 
and conclusions were to the truth. The undulating membrane 
he speaks of, is no doubt Professor Schultze's hyaline band, 
whilst he also observed internal currents of granules. 
Professor Schultze remarks that there are three types on 
which the holes for the emission of the hyaline protoplasm are 
arranged. The first presents us with long open slits on the 
surface of the frustule, corresponding with the raphe, and is 
seen in Navicula viridis, and its allied forms. The second 
type has the raphe closed, but with fine openings at either 
end — this is the case in Pleurosigma. The third type is the 
most common, existing in all those flat Diatomacese in which 
the raphe runs along the narrower edges of the frustule. In 
these there are numerous openings placed along the elevated 
ridge at the sides of the frustule corresponding with the 
raphe. This is seen in Nitzschia (fig. 4), Surirella, &c. 
The movements of the Diatomaceaa other than those of free 
locomotion are admirably explained by Professor Schultze's 
