10 THE VOYAGE OE H.M.S. CHAIXENGEE. 



part ill the system of Mr. Hyatt. ^ Again, Mr. Carter makes an exclusive use of it as to 

 tlie special subdivisions of his order of Psammonemata, following the principle of 

 " beginning with horny fibre sparingly cored with foreign bodies, in order to go to that in 

 which the core is more general, and finally to end with that in which the horny element 

 is scarcely visible, and the core of foreign bodies only held together by a minimum of 

 sarcode, like the spicules in the Holorhaphidota."'" That, as a matter of fact, all the 

 naturalists in question have been wrong in this proceeding is clear to every one who is at 

 all acquainted with the recent progress of spougiology ; but as to Mr. Hyatt, I must still 

 add that logically he has had the best grounds for the division of the genus Dysidea 

 (Sjjongelia) into two independent families. His dermal-membrane theory of the formation 

 of skeletal fibres is false ; the dermal membrane, as we know now, stands in no connection 

 with this formation. Furthermore, it is improbable even theoretically, and indeed more 

 diflicult to understand than the phenomenon itself, but having once adopted the idea 

 that in different sponges the secondary fibres are of quite difierent origin (those of his 

 Sjwngelia owing their formation to his " mesoderm," those of his Dysidea to his 

 "ectoderm"), he was certainly right in ascribing to this difi"erence the significance of a 

 family character. For this character would be an absolute character, while Carter and 

 Marshall have been sure of the contrary. Of course, the proceeding of Mr. Carter is 

 still comprehensible, since his system was devised before the important investigations 

 of F. E. Schulze were published, but the proceeding of Dr. Marshall is to me quite incon- 

 ceivable. He makes use of a quantitative distinction in order to characterise a family.^ 

 I am very well aware that the systematic definitions we give to the species, genera, 

 and accordingly to the families, particularly when young groujjs of animals are con- 

 cerned, must be according to circumstances more or less conditional. But this is the 

 privilege of natural arrangements. Is that of Dr. Marshall's Dysideidas a natural one ? 

 Surely not. Among his Dysideidje we find sponges with quite different internal organis- 

 ation. We find * there Oligoceras coUectrix, F. E. Schulze, a sponge whose canal system 

 follows the type of that of Spongidse; we fiud"^ there some representatives of the genus 

 Dysidea, whose canal system presents, according to Marshall, quite difierent characters — 

 those of a vesicular type; we find" there also sponges with a canal system arrantrcd 

 according to the so-called dendroid type, which has no more real existence than the 

 vesicular type; finally, we find^ there sponges whose canal system could not have been 

 made out, the specimens having been very badly preserved. Dr. Marshall calls F. E. 

 Schulze the most eminent spongiologist of the present time; he calls his sj)ongiological 

 papers briUiant; but the chief merit of F. E. Schulze consists precisely in having made 



1 Revision, &c., jiart ii. p. 482. - Ann. and Mag. Nat. Hist., ser 4, vol. xvi. p. 135, 1875. 



2 " Die Dysideiden siud Homscliwdinme bei deuen die auch alien iibrigen Horuschwammen in bolierem oder werin- 

 gercm Masse innewohneude Fahigkeit das eigene Skelett dm-ch aufgenommene Frerndkorper zu verstarkeu, den 

 hochsten Grad erreicht hat." — Loc. cit., p. 92. 



■• Loc. cit., p. 92. ' Loc. cit, p. 99. <= Loc. cit., p. 105. ' Loc. cit., p. 98. 



