414 NATURAL SCIENCE [December 
same mechanical effect would be produced in either case. Lauter- 
born is content to describe it as a viscous substance, though he 
apparently inclines to the belief that it corresponds to the jelly 
already described in Pinnularia, and believes that corroborative 
evidence for this view is furnished by an examination of Surrirella. 
The structure of the alae in S. calcarata, with the arrangement of 
the longitudinal and transverse canals have been already described. 
The displacement of foreign bodies along the clefts in the longitudi- 
nal canals has been long known, and it is pointed out that, although 
the protoplasmic strands surrounding the chromatophores in the 
transverse canals exhibit, in the living diatom, a well-marked 
reticular structure, the contents of the longitudinal canals are 
perfectly hyaline and can only be brought into view by staining. 
Thionin and methyl violet were used, after which the substance in 
question appeared as a granular contracted string, from which the 
plasma of the transverse canals was generally separated. 
With reference to the capability of diatoms to produce con- 
siderable masses of jelly under certain circumstances, it is pointed 
out that there are a considerable number of forms in which single 
cells are united into colonies of variable shape by gelatinous 
material (Eneyonema, Schizonema, Mastogloia, etc.). In other cases 
the cells are borne upon long gelatinous stalks, as in Achnanthes and 
Gomphonema, whilst, in auxospore formation, numerous diatoms, 
generally free from jelly, are known to secrete it very profusely. 
In places where diatoms are massed together, covering the mud on 
which they rest with a brown scum, it is only necessary to take a 
piece of the latter between the fingers in order to appreciate its 
slimy nature, due to the production of jelly by the living cells. A 
movement by the aid of a gelatinous material produced by the living 
cell is not confined to the Diatomaceae, but is found in other forms, 
both animal and vegetable. Desmids, eg. Closteriwm, secrete a gela- 
tinous thread by the help of which the cells are able to raise them- 
selves upon the glass walls of the culture vessels. In the form 
mentioned, the thread emerges through pores at the extremity of 
the cell, and can only be demonstrated by staining, or by the em- 
ployment of an emulsion of Indian ink. 
Again, in the case of Oscillaria, Lauterborn describes and figures 
the adhesion of foreign bodies to, and their movement in spiral paths 
along, the algal threads. As the Oscillaria moves forwards, a bright 
streak appears at the hinder end (visible in Indian ink, or by stain- 
ing) and lengthens as the Oscillaria advances; it is apparently to be 
regarded as consisting of a jelly-like substance separated on the sur- 
face of the algal thread and drawn backwards in a spiral manner. 
A very similar mode of progression is also met with in the Gregarines ; 
these, according to Schewiakoff, also produce a long glutinous track, 
. 
