The Strudure of Diatoms. By Br. J. H. L. FUgel. 519 



■will penetrate the interstitial molecules of thin membranes with the 

 greatest faciUty is known to every novice. Were one to suppose 

 or to search for holes with this experiment we should cancel every 

 investigation made during a century with regard to endosmose. 

 This point needs no refutation. I refer to what I said, pp. 487-8, 

 about the penetration of water into the valves, and it will be the 

 same with all other fluids. The further deductions by Miiller, 

 pp. 622-5, in connection with his flooding experiments are by far too 

 obscure for me. Even admitting the facts with regard to Pleuro- 

 sigma were as Miiller believes, that the chamber had an opening 

 outwards as with Triceratium, there is no reason whatever to 

 infer that the microscopical surface-image could be altered in air, 

 balsam, bisulphide of carbon, &c. The chambers whether elliptical 

 or spherical in connection with the wall-nod ale operate in the 

 one case as concave lenses, in the other as convex lenses ; whether 

 they have an entrance from outside or not is immaterial. If en- 

 trances do exist, but which up to the present have not been 

 observed, I would sooner admit that they lie on the inner side of 

 the membrane. In support of this statement is the analogy of 

 Finnularia and the collodion cast showing a delicate relief-image 

 of the inner side (6, p. 493). 



(3) Miiller seems to think (14, p. 76) that we ought to in- 

 vestigate the real condition of diatom structure indirectly, and 

 especially the Pleurosigma sculpture, and in illustration he 

 describes his investigation of Triceratium favus. On pp. 79-80 

 he has no hesitation in applying to Pleurosigma what he found 

 with Triceratium. This means, in other words, that everything 

 said by Flogel with, regard to Pleurosigma does not quite agree 

 with what I (Miiller) found out with Triceratium^ therefore the 

 former must be wrong ! 



(4) The fourth point is Miiller 's representation of a transverse 

 section of Pleurosigma (15, fig. 1 a and 1 &). He writes (p. 637) 

 that he succeeded in finding it amongst numerous sections, and 

 then he terms it (p. 621, and explanation of fig. on p. 641) 

 P. scaljyrum, with a sign of interrogation. What he has repre- 

 sented there is a fragment of a very thick transverse section of 

 P. halticum I I cannot avoid calling this a prodigious blunder. 

 For Miiller, after his researches with diatoms, ought to know that 

 the small delicate P. scalp-urn could never furnish such a colossal 

 transverse section, in whatever direction made. Further, on 

 p. 488, fig. 19, I have described and figured the transverse section 

 of P. scal'prum, and the fig. is on the same scale as the transverse 

 section of P. halticum, fig. 13. A confusion between these two is 

 utterly impossible. 



