ANIMAL NATURE OF DIATOME^. 421 



exhibiting a tremulous motion." Whoever has observed 

 many living Naviculce may yet, even after long study and 

 persevering laborious examination, find himself obliged to 

 confess, as I do confess, inability to decipher the complex 

 organisation ; but he may also declare, conscientiously, 

 that he has seen, in these, numerous phenomena perfectly 

 analogous to those presented by animals, and to vphich no 

 vegetable ever presents any similar. 



32. Amphiplt!URa. — Individua singularia navicularia 

 prismatica hngitudinaliter sulcata, apertura media nulla. 



Kiitzing observes that mere regard to similarity of form 

 caused this genus to follow the Navicula, though the 

 want of a median aperture excludes it from the Navi- 

 culese. He might have said the same of some Synedrce. 

 It is a circumstance worthy of remark, that on account 

 of the two projecting lines of the secondary surfaces, the 

 division cannot take place without a species of reduplica- 

 tion. The one of the three species which is sigmoid 

 {A. rigidd) is curved on the primary surfaces, and under 

 a double aspect manifests an analogy (not an affinity) 

 with the Achnanthese. Although the central perfora- 

 tions are absent, the terminal ones seem to remain in the 

 AmpJnpleura. 



33. Ceratoneis. — Individua navicularia libera sin- 

 gularia rostrata, prismatica, quadrangula; apertura media 

 distincta, terminalibus nullis. 



The rostrum only, Kiitzing says, distinguishes this 

 genus essentially from Navicula. The first species (C. 

 laminaris) differs but very slightly in form from some 

 NaviculcB, {N. cuspidata, N. rostrata,) but if the terminal 

 apertures be really absent in this and present in the 

 others, the organographic difference is great. Of the 

 other four species, one is sigmoid, [C. Fasciola,) one 

 contorted and spiral, (C spiralis,) and two merely arched, 

 {C. Closterium, C. Arcus). But in the last the symmetry 

 of the primary surfaces is remarkable, whence there 



