1898] THE MOVEMENT OE 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 

 Eauptfleisch 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 Midler agree in considering the protoplasmic threads to be 

 merely contracted portions of the plasmatic cell-body occupying the 

 inner chambers of the frustule. 1 



Methods of Collecting and Preserving Diatoms. — In 

 collecting, a spoon attached to a stick was employed for skimming the 

 brown diatoinaceous ooze off the surface of the mud, whilst in the 

 case of forms occurring at greater depths, e.g. Surrircl/a, 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/ Q 

 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 Biitschli, 

 which stain exceptionally well after fixing by this method. 



< Inly 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 chromatuphores was extracted, ami 

 any oil globules removed. The addition of a drop or two of sulphuric 

 ether and the application of a moderate 1 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 0. Miiller, in a paper which I have not yet read (Ber. Deutsch. Bot. Gcstll., xv. (1897), 

 Pp. 70-7S), 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. 



