1898] THE MOVEMENT OF DIATOMS 415 
which can be brought into view by the methods alluded to above. 
His illustrations show how great is the resemblance to the corre- 
sponding phenomena in the Desmidieae and Oscillaria. 
In concluding the part of his work dealing with the move- 
ment of diatoms, Lauterborn briefly criticises a theory advanced by 
Hauptfleisch in 1895. In opposition to other observers Hauptfleisch 
would locate the organ of locomotion in Pinnularia in protoplasmic 
threads issuing from pores on the longitudinal edges of the diatom. 
These pores, however, are apparently non-existent, and both Lauter- 
born and Miiller agree in considering the protoplasmic threads to be 
merely contracted portions of the plasmatic cell-body occupying the 
inner chambers of the frustule.’ 
Methods of Collecting and Preserving Diatoms.—In 
collecting, a spoon attached to a stick was employed for skimming the 
brown diatomaceous ooze off the surface of the mud, whilst in the 
case of forms occurring at greater depths, ég. Surrirella, a small 
drag-net was found useful for bringing samples of mud to the surface. 
This latter was placed with water in shallow glass vessels sheltered 
from direct sunlight, and after resting for about twelve hours the 
diatoms appeared in masses on the surface of the mud, whence they 
were readily transferred by means of a pipette to the fixing-fluid. 
Among fixing reagents, Flemming’s chromo-aceto-osmic acid, and 
sublimate in either water or alcohol solutions, demonstrated the most 
delicate structural features of the nucleus and cytoplasm during 
division. Picro-sulphuric acid followed by a haematoxylin stain gave 
excellent pictures of the chromatic elements of the nucleus. A 1/ 
osmic acid solution served, in unstained preparations, to bring out 
the arrangement of the cytoplasm, the chromatophores, and other 
inclusions in the cell. A 45°/ solution of iodic alcohol is recom- 
mended for the study of the so-called ‘red granules’ of Biitschh, 
which stain exceptionally well after fixing by this method. 
Only large forms could be removed individually under the dis- 
secting microscope and by means of a capillary tube; the smallest 
forms were taken up in the mass by a pipette and at once placed in 
a tube containing the fixing solution. Here they remained for about 
fifteen minutes, after which, the fixing fluid being decanted off, they 
were well washed in water, and afterwards passed, through alcohols of 
increasing strength, into absolute alcohol, where they remained until 
all the colouring matter of the chromatophores was extracted, and 
any oil globules removed. The addition ofa drop or two of sulphuric 
ether and the application of a moderate amount of heat facilitated 
this process. Afterwards, the material was passed through alcohols 
of decreasing strength into distilled water, in readiness for staining. 
The most useful stain was a weak solution of Delafield’s haema- 
toxylin, but it was necessary to control the process under the micro- 
scope in order to prevent overstaining. Alum- and borax-carmine 
were also tried, but with decidedly inferior results. Safranin was useful 
1 OQ, Miiller, in a paper which I have not yet read (Ber. Deutsch. Bot. Gesell., xv. (1897), 
pp. 70-78), seems now to regard movement as taking place by means of currents of a mucila- 
ginous substance projecting from the raphe. See Jour. Roy. Micro. Soc., 1897, p. 234. 
