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 Sitrrirella. 

 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 {Encyonema, Schizonema, Mastogloia, etc.). In other cases 

 the cells are borne upon long gelatinous stalks, as in Achncmthes and 

 GompJwncma, 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, e.g. Closterium, 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, 



