90 GENERAL HISTORY OF THE INFUSORIA. 



&c. But, as Menegllim remarks, '' he might have added the more appropriate 

 instance of the Desmidieae, which would be very closely allied to the Diatomege, 

 if the latter, like the former, could bo referred to the vegetable kingdom. If 

 not equal in constancy and regularity, the Desmidieae display a greater degree 

 of complication: and we must remember the different nature of their substance; 

 for in the vegetable cell, when lime or silica predominates, the wall becomes 

 imiform and regular." 



4. Multiplication by self-division was at one time cited by Ehrenberg as 

 peculiarly an animal phenomenon, — a notion at variance Avith the observations 

 of every naturalist, and now requiring no refutation. However, Meneghini 

 has more recently advanced the statement that an essential difference in the 

 process of fission prevails between the Diatomeae on the one hand and the 

 Desmidieae and Algae in general on the other, applying to the former modifi- 

 cation (in accordance "with Brebisson's views) the term deduplication, to the 

 latter reduplication. To extract his remarks {op. cit. 368) — " Division is 

 always longitudinal, and takes place underneath a fine external sihcious 

 membrane, by the formation of contiguous diaphragm walls which divide the 

 internal ca\T.ty. Thus the contents are longitudinally divided ; and this divi- 

 sion is complete if the two new individuals detach themselves and so acquii^e 

 individual liberty. It is imperfect if the fine silicious persistent membrane 

 and the secreted gelatinous substance retain them connected together. This 

 mode of reproduction (which Brebisson distinguished by the name of dupli- 

 cation and deduplication, from the reduplication of Desmidieae) 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 ciix'iunstantial description peculiar to various forms. It is 

 only after having established facts relative at least to the principal generic 

 tj-pes, that we can establish, on a scientific basis, the general idea of multi- 

 plication by duphcation. A few observations suffice, however, to prove that 

 this does not occur in so simple a manner as we are taught to believe, by 

 compaiing it with that in vegetable cells. In the Achnanthidia, for example, 

 it is described and figured that the principal surfaces, which occupy the inter- 

 mediate 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 new inferior individual, and the inferior 

 one of the superior. My observations convince me that the affair does not 

 proceed vsith so much simpUcity. I have often seen the two lateral valves 

 separated, and the intermediate space thus largely amplified. In other cases 

 there appeared only a new inferior valve complementary to the superior, the 

 inferior individual thus remaining incomplete. Finally, in others, between 

 the complete superior individual and the incomplete inferior valve, there 

 appeared a new individual with both its valves, but nearer together, smaller, 

 finer, with lines much less distinct." In short, " in this phenomenon there 

 is more complication than that of a simple cellular deduplication." 



5. In a previous page (p. 88) we have quoted Schleiden's notice of a dif- 

 ficulty in the way of recognizing Diatoms to be plants. It is one likewise 

 which has presented itself to others, for instance, to Prof. Bailey and Mene- 

 ghini. ^' If we suppose them to be plants," says the latter writer, " we must 

 admit every frustule, every Navicida, to be a cell. We must suppose this cell 

 with walls penetrated by silica dev'eloped within another ceU of a different 

 nature, at least in every case where there is a distinct pedicle or investing 

 tube. In this silicious waU we must recognize a complication certainly im- 

 equalled in the vegetable kingdom." (op., cit. p. 372.) 



