I 



AND LIFE-HISTORY OF DIATOMS. 421 



Spirogyo'a, whilst the last-named author has also figured and 

 described intracellular fibrils in Mnium undulatum which exhibit 

 a delicately-beaded structure, are generally arranged parallel to 

 the long axis of the cell, and contain minute oscillatory granules. 



Most prominent amongst the cell contents in the Diatomaceae 

 are the chromatophores, structures which are invariably present. 

 Their colour is, in most cases, a beautiful golden brown (more 

 rarely olive green), due to the fact that the chlorophyll of the 

 endochrome plates is mixed with a brown colouring- matter, the 

 so-called diatomin. 



To attempt any description of the various forms of chromato- 

 phores in different genera of Diatoms would extend this paper 

 beyond permissible limits, but certain other less prominent cell 

 inclusions must be briefly noticed. 



The bodies known as Pyrenoids were first discovered in the 

 Diatomaceae by Fr. Schmitz, first of all in marine forms, and 

 subsequently in many freshwater genera, though it should not 

 be forgotten that Pfitzer had previously described and figured, 

 in Cymhella and Gomphonema, definitely-formed bodies which 

 correspond, in part at any rate, to the structures subsequently 

 designated pyrenoids by Schmitz. 



The fresh-water Diatoms in which the latter observer detected 

 these bodies belonged to the genera Frustulia, ■ Colletonema, 

 Cymhella, Encyonema, Brebissonia, Anomoeoneis and Gomphontma. 

 Lauterborn's observations extended only to Cymhella and Surirella. 



Cymhella cuspidata possesses a single large pyrenoid occupying 

 a depression in the chromatophore on the most convex side of 

 the Diatom (Fig. 3, py). It may be stained with safranin 

 and other aniline dyes, but it is unaffected by Delafield's 

 haematoxylin in material fixed with chromo-aceto-osmic acid. 



The pyrenoids in Surirella calcarata "are numerous, and lie 

 embedded in the lobular extensions of the chromatophores, 

 usually one pyrenoid to each lobe (Fig. 4, py). During life they 

 appear as bright rounded spots, not particularly sharply differen- 

 tiated from their surroundings, but become for a time much more 

 prominent, owing to the contraction of the chromat02)hores, 

 if the frustule is damaged, appearing then as sharply-defined, 



JouRN. Q. M. C, Series II.— No. 52. 28 



