Bacillaiia.} infttsoeial animalcules. 219 



conferva-like forms are not composed of long slender and filiform 

 bodies, like plants, but of short and broad filiform portions Some- 

 times tlie self-division is from back to front, or from side to side ; the 

 single creatures are then band-like, or half-moon-shaped. 



In Navicida, Ehrenberg has described a locomotive organ possessing 

 the power of moving in any direction, and accommodating itself to 

 any form, similar to that cnrious muscular organ, the tongue, in 

 animals, or to the foot-like process of snails. 



The shells of these creatui'es are often sculptured with deep 

 flutings ; where this occurs, the inside of the shell is not always 

 smooth, but follows the form of the exterior : thus the strength is 

 gi'eatly increased, while the quantity of solid material employed in 

 their construction is not augmented. The flutings (striae) in the 

 living specimens being filled with coloured matter, are discerned 

 with difficulty, and hence they are almost unknown. In the fossil 

 state, the shells are empty, and then the flutings and other indenta- 

 tions become distinctly Adsible. I have, therefore, in the engravings 

 illustrating this family, selected dra-ndngs of several in both states, 

 so that the reader may form a clear conception of their true characters, 

 while the interest attached to the family generally is so great, and 

 we possess so few drawings of its various species, that I have been 

 induced to extend the number of illustrations considerably. The 

 order of their arrangement differs from that given in the plates of Die 

 Infusionsthierchen ; in that work the species and genera are placed in 

 plates indiscriminately, and no regular aiTangement is observed. As 

 some fossil specimens have been discovered since Ehrenberg' s great 

 work appeared, I have had drawings of the finest I could procure, 

 made for me ; some of them are the last productions of my fiiend, 

 the late E. Bauer, Esq. ; so that the numerous illustrations of this 

 family, whether the members be considered as animal or vegetable, 

 will, I believe, be highly acceptable both to the botanist and 

 zoologist. 



The remarks in the last paragraph refer to the engravings of the 

 first edition, all of which are retained in the present one, while 

 most of the mimerous figures in Plates 13 to 20, are additional illus- 

 trations of the Bacillaria. 



In this family we are not only presented with the simplest foiTns 



a 2 



