^aDlcutacea.'] inpitsohial ANiMALCUtES. 395 



and retracted through openings in the lorica, met witl\ any support 

 from other naturalists. Some few, indeed, have seen hair-like appen- 

 dages to the lorica of Surirella Gemma, and also to that of some 

 other JJiatomece, but none have witnessed any power of motion in 

 them, and their presence would seem almost accidentaL (See note 

 on Surirella Gemma, by the Eev. W. Smith, p. 404.) Dujardin 

 affirms, as the result of most minute and painstaking investigations, 

 that foot-like processes, and moving cilia, have no existence in any 

 Navivida. 



Ehrcuberg's assumption, that the clear vesicles, often seen in the 

 interior of Xavicuh, are seminal vesicles, is recognized by no other 

 naturalist. Kiitzing says they are oil-vesicles, without any true 

 enclosing wall, ccciu'ring at hazard, capable at -duj time of coalescing 

 on approximation, and distributed irregularly, and in varying abmi- 

 dance, amid tlie contained amylaceous clilorophyl of the lorica. 



In seven species of Kavicula, Ehrenberg proved, to his mind, the 

 stomach-like nature of tlie globules seen in thcii" interior, by the 

 supposed visible imbibition of an artificially coloured solution in 

 which the Naviculce were placed. These so-called stomach vesicles 

 vary in number and position in the same species ; their distribution 

 is, for the most part, quite irregular, and sometimes they are entirely 

 wanting. This last circumstance, Kiitzing remarks, is opposed to 

 the belief in then- digestive functions, for surely such important 

 organs as stomach should never be absent. Moreover, other ex- 

 perimenters have failed to get any colouring matter introduced 

 within the lorica of Naviculce. 



lioth Kiitzing and Ehrenberg coincide in the opinion of the 

 ■ circular spots of the lorica being actually pores; and the former 

 describes them as furnishing an exit for the gelatinous substance 

 which is found to invest some Naviculce, and is especially remarkable 

 in the case of those genera having, as Ehrenberg terms it, a double 

 lorica, such as Schizonema. In opposition to this notion of the lorica 

 being porous, Schleiden gives engravings to prove that the apparent 

 openings are but depressions of the sm-face, and have no communica- 

 tion with the interior. Dujardin affirms, on the contrary, that they 

 are elevations (see p. 399, and Plates 19 and 20.) 



The lorica of Navicula, as of other Bacillaria, is generally con-" 



D D 2 



