8 THE VOYAGE OF H.M.S, CHALLENGER. 



horny lamina, and Flemming/ like Carter,^ emphatically denies their occurrence in the 

 core of the fibres. My own endeavours to discern them there have been equall}^ 

 unsuccessful, and this not only vnih regard to lanthella, but also with regard to Verongia, 

 Aplysina, Darwinelkt, and Aplysilla, in which connection I should lay stress on the fact 

 that the specimens of Ajylysilla sulpharea, kindly placed at my disposal by Prof. F. E. 

 Schulze, have been examined both in the living state as well as preserved by the methods 

 recommended by Dr. v. Lendenfeld. In no single case have I been able to discern in 

 the central canal of the horny fibres anything that might be regarded as spongoklasts. 



Again, Dr. Vosmaer states the same with respect to his Velinea gracilis.^ And far 

 from supposing that Dr. v. Lendenfeld has described what he did not see, I feel 

 convinced that he has misinterpreted what he did see. It may be said that what 

 does not occur in lanthella or Aplysilla may be characteristic of Dendrilla. Such a 

 possibility indeed is not excluded, but it is extremely improbable. For, firstly, Dendrilla 

 seems to be so closely allied to Aplysilla that both these genera wiU probably in time 

 be united into one ; and secondly, because with an instrument like the microscope one sees 

 very often precisely what one desu-es to see, and that Dr. v. Lendenfeld has been desirous 

 to find out his spongoklasts is beyond any doubt, the spongoklasts having been for him 

 a logical necessity. He refers in his above-mentioned memoir to the statements of F. E. 

 Schulze as to the fact that, though on the whole the old larger skeletal fibres of Aplysina 

 aerophoba must be called thick-walled, the young ones of small diameter on the contrary 

 thin-walled, still the diameter of the central pith-substance in larger fibres is comparatively 

 greater than that of the small ones. He tells us further that the same can also be said 

 with respect to the Aplysillidfe which he had for examination, and he deduces from this 

 the conclusion that hand in hand with the growth of the fibre its pith-substance increases 

 also.* If all this be so, indeed, without the theory of spongoklasts, the phenomenon would 

 be quite inconceivable. I must, however, deny the reliability of the statements in question. 

 The fibres of the representatives of the genera lanthella,^ Verongia, and Luffaria have 

 been submitted by me to the most careful examination, and I must state that in aU the 

 above specimens I found very often fibres of the same size but with difi"erent diameters of 

 the central canal ; and since I find also that this is the case not only as regards the fuUy 

 developed fibres but also those in embryonic condition, I believe that the phenomenon we 

 are speaking of is easily explained without any reference to spongoklasts, if we assume that 

 the pith-substance is a product of the p>olygonal spongoblasts, and the laminar horny sub- 

 stance the product of those of elongated shape, and that the differences in diameter of the cen- 

 tral canals are dependent upon their having been deposited broad or narrow. The second 



1 Loc. cif., p. 4. - Loc. cit., p. 115. 



3 Loc. cit., p. 441. ■• Loc. cit, p. 290-293. 



5 I should call attention to the fibres constituting the skeleton of the stem of this sponge ; some of them are far 

 thicker than the piimary fibres of its leaf-like part, but, nevertheless, with the diameter of the central canal not only 

 considerably smaller than that of the primary fibres just mentioned, but occasionally not larger than that of a Spongeiia. 



