8 



HARD WICKE ' S S CIE NCE- G O SSI P. 



have i^reviously only been vaguely figured, and cause 

 a pleasure inexpressibly sweet and gratifying, {un 

 plaisir ineffable et les plus douces joiiissances). 



Forms and organs. — By means of the organisation 

 of those animalcules we are able to divide them into 

 two classes and to subdivide them into six families, 

 viz. the Navictihr, the Cosmaria:, the Euastrea, the 

 Closterue, the FragilaricE, and Arihrodicz. The 

 three first families have a brittle (fragile), and the 

 other a flexible integument (Corda's reason for placing 

 the P^agilarias in the latter class was, no doubt, on 



resembles the shell of the mussel, and is composed of 

 one or two transparent siliceous plates which enclose 

 the animal. The univalve cuirass is a single plate 

 (feuille) rolled on itself (the forms Corda calls uni- 

 valves are Epitheniia, Navicula, Fragilaria, Syrinx, 

 &c., F.K.). When the edges coalesce the whole of the 

 animalcule is covered, excepting where there are a 

 few small apertures. This cuirass appears to be 

 either smooth, as in Friistiilia appcndiciilata (fig. S), 

 or grooved, as in Navicula costata [Epithemia Wester- 

 mannia. F.K.), where the grooves i^adiate from the 



Fig. 5. — Frus- 

 tidia appendi- 

 ciilaia[Coida). 



IV 



u 



Fig. 6. — Fnisinlia viridescetts 

 (Corda). a a, pedal organs. 



Fig. 4. — Phary>igogiossa sigtiioidea (Corda). i. a, plug toj 

 canal ; b, head ; c, anal termination ; d, sexual protuber-| 

 ances ; y] intestinal canal ; _^, anus. 2. Head (side view),! 

 It, plug ; b, cleft in cuirass with fuot protruded ; y, intes-^ 

 tinal canal; i, contents. 3. Head (front view), a, plug ; 

 h, foot ; d, sexual eiicrescence. 4. Posterior extremity ; 

 the letters refer to the same parts as in 2. 5. a'^, plug 

 protruded through aperture a^ and beyond the canaiy"; 

 /', the part surrounding the ligament to which it is 

 attached. 



Fig. S.—Surire/la Venus (Corda), = 6". striatula (Ehr.) 

 a, a, cuirass ; b, hinge ; c, mantle; d, notch or slit in 

 interior membrane ; e, contents brown or green. 



Fig. 7. — Scalptruni striatian (Corda). a a, pedal organs ; b, central opening passing through the brown 

 contents d ; e, longitudinal rays between the sides c of the cuirass. 



account of the flexibility of the filament, although it 

 is somewhat contradictory to place a genus called 

 Fragilaria on account of its fragility, in a class distin- 

 guished by its flexibility. F.K.), but in order to recog- 

 nise the form of these creatures, it is necessary to de- 

 scribe all the organs of which they are composed. The 

 external integument (epidermis) of these animalcules 

 is of two kinds ; one is a siliceous shell, transparent 

 and glossy, and which is termed the cuirass (lorica), 

 or the cuirass is absent and the epidermis is naked. 

 The cuirass, in tl e majority of these animalcules, 



umbilicus which is placed on one side of the centre 

 of the cuirass or simply at the side ; this umbilicus is 

 sometimes large and elevated, as in N. costata, the 

 sides of which are furnished with cilia. In Navicula 

 and Frustulia the cuirass is smooth on the lower 

 surface (partie inferieure), and is usually quadran- 

 gular or parallelogrammic ; this is called the pedal 

 surface, and by which the two animalcules always 

 adhere (fig. 9). 



In the Diatoms, e.g. D.fenestratiim (fig. 10), the 

 cuirass is flattened and crenate at the margins ; the 



