ANIMAL NATURE OF DIATOME.E. 439 



simulate the tubes themselves ; for the coagulation could 

 not produce regular tubes, and moreover the presence of 

 these tabes is always accompanied by a regularly seriated 

 disposition of the Naviculae. There can only remain 

 the supposition already mentioned, that besides the pre- 

 sence of a single enclosing tube, as in Monnemce, and 

 that of partial tubes, characteristic of the Schizonemce, 

 there may be a third condition, that of a continuous 

 mucous substance in which single Naviculae or the 

 entire series of them may be imbedded. And this third 

 condition according to the changes induced, and es- 

 pecially in consequence of desiccation and perhaps of the 

 use of chemical reagents, may simulate either one or both 

 these opposite conditions. Finally, in respect to the 

 partial tubes, I perceive that frequently, where they 

 remain empty of Naviculse, they are so contracted and 

 contorted as to appear like nothing but the finest threads, 

 which often unite the remaining Naviculae together by 

 their apices. And the condition I have before described, 

 when treating of the filiform appendages with which 

 Naviculae sometimes appeared to be furnished (v. S. 

 Hlyricum^} is the same which is seen also in the figure 

 given by Ehrenberg of his Naunema Agardhii. Therefore, 

 without pronouncing any judgment on the fibres indi- 

 cated by Kiitzing, I express merely my own supposition 

 that their apparent presence may be produced by the 

 partial tubes themselves. 



To the organic condition of the so-called internal 

 spermatia, prudently noticed by Kiitzing, I think we 

 ought to refer the circumstance of the great variety of 

 dimensions presented by Naviculse, not only in the same 

 species, but very frequently in the same specimen. Varie- 

 ties are often met with in different individuals which an 

 attentive examination compels us to recognise as belonging 

 to the same species, while within the same thread all are 

 found to be equal. In the Schizonema, on the other 

 hand, we find, mixed amongst the larger Naviculae, others 

 that are less, and some very small, scarcely visible with 



