336. PROF. EHRENBERG ON ANIMALS OF THE CHALK 
When I published my first communications on the species of — 
the genus Dictyocha, I remained in doubt whether they were 
really animals, or only fragments of animals, or parts of sponges. 
At all events, they were very regularly shaped corpuscles, con- 
sisting of silica, easily recognised by their remarkable form, 
which appeared to characterize the chalk marl, and not alto- 
gether unnaturally to join on to the forms of Arthrodesmus and 
Xanthidium of the Infusoria*. Careful attention to all cireum- 
stances had guided the first opinion with tolerable correctness. 
The knowledge of the living animal Dictyocha Speculum las not 
changed the view then entertained. They are evidently poly- 
gastric animalcules of the family Bacillaria, which are inwardly 
coloured green by numberless green granules, or according to 
analogy, bear egg-sacs full of green ovules, and have a very slow 
creeping motion. Scattered minute vesicles in their interior 
indicated, as distinctly as in many other Bacillarie, the poly- 
gastric structure of the intestines. External locomotive organs 
could not be detected; it was however ascertained that the six 
long spines of the circumference are not inclosed by the soft 
body, but that this merely fills the inner space of the small hard 
basket-shaped portion of the animal, at the borders of which 
these spines project. 
The genus Coscinodiscus was, in 1837, in my first memoir on 
its existence in Oran and Zante}, immediately placed in the 
family of the Arcelline, and the first form characterized as Ar- 
cella? Patina. But even in 1838, the further examination of the 
fossil fragments had led me to believe that probably two of these 
round plates might always belong to one individual animal. They 
were therefore subsequently, although always with doubt, placed 
under the family Bacillarie, first with a mark of interrogation 
as Gallionellat, then in the neighbourhood of the Gallionelle §. 
The finding of four existing species has set aside all doubtand fully 
confirmed the latter view. These forms, in the living state, do not — 
like Gallionella constitute long filaments resembling articulated — 
* Both in the illustrated work on Infusoria, concluded in 1838, p. 165, and — 
in the memoir on the Chalk, printed in 1839, p. 73, the nature of these bodies 
remained doubtful, but they were in 1837 (Report of the Acad. 1837, p. 61) as- 
serted to be nearly allied to the genus Arthrodesmus. These forms of the sec- 
tion of the Desmidiacee among the Bacillarie have, by their siliceous shield, the 
peculiar interest, that they present a new obstacle to our viewing the soft-shelled 
Desmidiacee as plants on account of their organization being difficult to recog- 
nise and most of them having but very little motion, in as far, namely, as the other 
silica-shelled bodies, the Naviculacee, exhibit very distinct animal characters. 
+ Report of the Acad. 1837, p. 60. Die Infustonsthierchen, p. 134, mo 
lished 18388. t Lbid.-p. 111. § Ibid. p. 172. 
