368 ANIMAL NATURE OP DIATOME^. 



it has not the odour of horn, but of aniseed, and the 

 products of distillation have rather an acid than an alka- 

 line reaction. 



According to Kiitzing, the propagation or multiplica- 

 tion of Diatomeae takes place in three modes ; by deve- 

 lopment of the gonimic substance, by division, and by 

 formations analogous to seeds or gemmules. 



The first is merely suppositious, and therefore requires 

 no further notice. 



Division is always longitudinal, and takes place under- 

 neath a fine external siliceous membrane, by the formation 

 of contiguous diaphragm-walls which divide the internal 

 cavity. Thus the contents are longitudinally divided. 

 And this division is complete if the two new individuals 

 detach themselves, and so acquire individual liberty. It 

 is imperfect if the fine siliceous persistent membrane, and 

 the secreted gelatinous substance retain them collected 

 together. This mode of reproduction, (which Brebisson 

 distinguished by the name of duplication and deduplica- 

 tion from the reduplication of Desmidiese,) deserves the 

 most attentive observation. The foregoing exposition 

 presents the fact in its most rude and superficial general 

 appearance, and makes us feel acutely the want of a more 

 circumstantial description peculiar to various forms. It 

 is only after having established facts relative at least to 

 the principal generic types, that we can establish, on a 

 scientific basis, the general idea of multiplication by dupli- 

 cation. A few observations suffice, however, to prove 

 that this does not occur in so simple a manner as we are 

 taught to believe by comparing it with that in vegetable 

 cells. 



In the Achnanthidia, for example, it is described and 

 figured that the principal surfaces, which occupy the 

 intermediate space between the two superior and the 

 inferior valves, commence by presenting fine transverse 

 lines, and next a strong longitudinal line along the 

 middle ; then there appear two new intermediate valves 

 contiguous to each other, the superior (valve?) of the 



