474 ANIMAL NATURE OF DIATOME^. 



thickness of the wall, the cavity of which appears as 

 a furrow, or rather as a perforation, at the extremities. 

 The oval aperture (fenestrd), which is visible in the 

 middle of the secondary surfaces, belongs to them in 

 appearance only, as in the preceding genera. It is only 

 seen because of the transparency. In Grammatophora, 

 also, the appearance of interrupted vittae, is produced by 

 the presence of diaphragms pierced by an ample central 

 elliptical perforation, and containing a distinct canal along 

 their attachment to the wall. Ehrenberg, too, describes 

 these diaphragms, which divide the internal cavity 

 regularly into three distinct compartments. This ar- 

 rangement is also shewn by heat, and by acids ; and the 

 various portions separate themselves so neatly, that we 

 may, in a certain manner, effect a most accurate dissection. 

 In this genus, these diaphragms have the characteristic 

 condition of very various degrees of flexature, which are 

 constant in each species, and impart to them the most 

 elegant appearances. In the deduplication, the line of 

 division between the new individuals, and the fine lines 

 which form the boundaries of the two new lateral surfaces, 

 precede the appearance of the corresponding diaphragms. 

 These are the fine lines delineated by Kiitzing within the 

 vittae, and regarded by him as the internal margins of 

 the canals, in which he believes the vittae themselves to 

 meet together. The deduplication of Grammatophora 

 greatly resembles that of Aclmantlddium. 



Ehrenberg describes the internal substance as consisting 

 of a central transparent and colourless body, containing 

 small gastric vesicles, and terminated at each extremity 

 by three-lobed dark-green appendages, which project into 

 the three corresponding cavities. The cushions (cuscinetti) 

 or hinges that retain the frustules in connection are 

 very evident, in all the thirteen species of this genus, as 

 in the Tabellaria fenestrata ; and this remark goes to 

 confirm what we have said of that species. 



The family of Tabellariea3 (Tetracyclus, Tabcllaria, 

 TerpsiniJe, and Grammatophora} constitute by themselves 



