2 THE VOYAGE OF H.M.S. CHALLENGER. 



itself all the others, concerns the systematic arrangement of the class Calcarea, proposed 

 by Prof. Hseckel in his monograph, Die Kalkschwamme. 



Although it is twelve years since this work made its appearance, yet no serious attempt 

 has been hitherto made to criticise Prof. Hasckel's systematic principles, although there has 

 been no want of consciousness that such an attempt w r as desirable. Some zoologists, it is 

 true, captivated by the ingenuity of the system established by Haeckel, not only proclaimed 

 the Monograph an " Epoche machendes Werk " (Keller), which I quite agree with, but 

 went so far as to express their conviction that there could be nothing further added to 

 the natural history of the class Calcarea, all having been done by the illustrious professor 

 of Jena. Other voices, however, were heard, which spoke of the necessity of a revision ; 

 as for instance, those of Leuckart, P. Wright, and more decidedly Metschnikoff and Claus. 



A complete revision of all the Calcarea described up to this time is at present 

 scarcely possible. The originals are scattered over all Europe, if not over the whole 

 world, and some of them are not to be obtained at all. I have done my utmost in 

 this direction, and I think that, including the Challenger specimens, the number of forms 

 at my disposal is sufficient to permit me to hope that the systematic arrangement of 

 the group Calcarea here proposed will serve as a sufficiently sure basis for further 

 investigations. 



I limit myself in this paper to a revision of the families and genera, this being the 

 most important part of the task. With respect to the species established by Hseckel 

 and later investigators, I am disposed on the whole to accept them. There are among 

 them some doubtful ones, but a discussion of these would lead me beyond the range of my 

 proper work, and I defer it to another ojyportunity. I think it also superfluous to give here 

 a historical report of the literature of the group. Prof. Hasckel's Monograph gives this 

 very amply up to the date of its publication, and the memoirs of the last twelve years 

 being principally embryological, I shall refer to them, when necessary, in the sequel. A 

 short historical report is also to be found in Dr. Vosmaer's paper on Leucandra aspera? 



In accordance with the above, I propose to divide my memoir into two chapters ; the 

 first will be devoted to general morphological and systematic questions, the second to 

 the description of the forms collected during the cruise of the Challenger. 



1 Aankekingen over Leucandra aspera, &c, Leiden 1880, pp. 1-34. 



