Naviculacea.'] inpusortal animalcules. 893 



leaf, the organic matter is consiiincd, and tlie siliceous lorica left 

 clear and free. The gelatinous and diaphanous body of these ani- 

 malcules occupies the whole of the interior of the lorica, and has, 

 near the centre, a sharply circumscribed colourless bright spot. In 

 N. fulva, an organ of locomotion has been seen by Ehrenberg, which 

 he describes as a fleshy, undivided sole-like foot, proceeding from the 

 central opening, and similar in appearance to the locomotive organ 

 of snails. The side of the body where this foot-like process emanates, 

 is called the ventral surface of the animalcule. This foot not only 

 answers the purpose of allowing it to creep, but the animalcule, 

 when at rest, can draw objects to it, and push things away by it. 



"VMiether the two openings on the ventral surface are mouths, and 

 the two on the back apertures for respiration, is undecided ; but the 

 opening on the back, opposite the central ventral opening, is sup- 

 posed by Ehrenberg a sexual one. No direct demonstration of the 

 nutritive apparatus has yet been effected by using coloured food, 

 though numerous scattered and coloiu'less vesicles are to be seen 

 within the bodies of several species, which indicate polygastric 

 structure ; but what Corda took for an alimentary canal (in Pharyngo 

 glossa) was merely the dark central longitudinal furrow of the lorica. 

 This genus is more complex in its structure than the two preceding ; 

 and many consider these beings as animals. The green, yellow, and 

 brown colouring matter in their interior, supposed to be ova, occurs 

 in the form of broad plates or fillets, fi'om two to four (8 ?) jointed 

 together in the middle. These plates take the exact form of the 

 interior of the shell, filling the cavities of the flutings, furrows, or 

 striae. In many species, two or four round vesicles are seen, which, 

 although they are not changeable in form, or contractile, yet are 

 sometimes present and sometimes absent, ana are probably analogous 

 to small seminal glands. Many Navimla multiply by spontaneous 

 self-division, in which case it is invariably longitudinal, and dorsal, 

 or lateral ; the division taking place beneath the hard epidermis, as 

 in GaUionella and Achnanthes, and the lorica separating afterwards. 

 It is seldom in this genus that a second self-division commences 

 before the first is complete and separation takes place ; indeed, species 

 whose individuals separate into four, shoxild be placed in Fraxjilaria. 



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