410 NATURAL SCIENCE [December 
Siebold, Dippel, Borscow, and particularly Mereschkowsky, regarded 
the cell movement as the result of an osmotic phenomenon, supposing 
water to be imbibed at the anterior end of the diatom and expelled 
with greater force at the hinder extremity, the recoil serving to 
propel the cell onwards. 
Biitschli and Lauterborn worked together at the subject, and 
the former published a preliminary account of their researches, which 
was adversely criticised by O. Miiller. A reply from Lauterborn 
drew a further communication from Miiller, and this is dealt with 
in the work under consideration, where the Biitschli-Lauterborn 
observations and inferences are given at length, with a detailed 
criticism of Miiller’s objections and theory. ‘The observations de- 
scribed and illustrated by Lauterborn first claim attention, and will 
be best given as nearly as possible in his own words. 
When large examples of Pinnularia are brought into a concen- 
trated emulsion of Indian ink,! the majority of the diatoms present 
at the first glance a very striking appearance, each being surrounded 
by a broad, bright, and sharply defined border, within which the 
smaller granules of Indian ink do not penetrate. In a surface view 
this halo usually follows the contour of the frustule at a distance 
equal to about half the width of the valve; but when the lateral 
aspect of the diatom is turned towards the observer, this clear border 
is seen to be interrupted in a symmetrical manner at both ends of 
the cell, and also in the vicinity of both central nodes (Fig. 8); here 
the granules of Indian ink approach close to the cell-wall. 
The appearance just described is interpreted by Lauterborn as 
pointing to the existence of an enveloping layer of hyaline jelly, so 
remarkably transparent, and possessing a refractive index correspond- 
ing so closely with that of the surrounding water, as to be com- 
pletely invisible in clear water, even when examined with the best 
lenses.” Miiller denied the general presence of a gelatinous envelope 
in the sense advocated by Biitschli and Lauterborn, stating that the 
clear border only appeared after a long sojourn in the Indian ink 
emulsion, and that it was absent in the living but completely 
motionless cell. He, however, subsequently admitted the existence 
of a gelatinous envelope. In answer to Miiller’s objections on this 
point, Lauterborn asserts that the hyaline border becomes visible as 
soon as the diatoms are brought into the emulsion, and also states 
that he has often seen Pinnulariae, surrounded by the transparent 
envelope, remain for hours without the slightest movement. 
The presence of a peculiar and characteristic streaming move- 
1 Lauterborn recommends that the Indian ink should be rubbed up in the water in 
which the diatoms have been cultivated, and also that specimens from old cultures 
should not be employed in studying movement. 
2 A gelatinous envelope of similar transparency has been observed in a pelagic form 
of Cyclotella comta. 
