706 PROF. A. DENDY AND MR. R, W. H. ROW ON 



any of its predecessors, and we have made it tlie basijs of the classi- 

 fication here proposed. 



In 1896 Minchin published a paper entitled " Suggestions for 

 a Natural Classification of the Asconida?," which may fairly be 

 said to mark a new departure in the taxonomic study of the 

 Calcarea, in that it introduces for the fii'st time the idea of the 

 position of the nucleus in the collared cell as a character of 

 taxonomic importance, a character which has since pr-oved, in 

 our opinion, to be of great value. We have not been able, how- 

 ever, to follow Minchin completely in those modifications of 

 Dendy's classification of the group which he proposed, partly in 

 the paper referi-ed to, and partly in his well-known article in 

 Lankester's ' Text-book of Zoology ' [1900]. 



In 1898 Bidder, in a paper on "The Skeleton and Classification 

 of Calcareous Sponges," proposed to carry out Minchin's ideas 

 with regard to the nucleus of the collared cell to their logical 

 conclusion, and to divide the Calcarea into two great groups 

 accordingly — Calcaronea and Calcinea. Although not actually 

 adopting this division, which we consider to be somewhat pre- 

 mature in the present state of our knowledge, we have ourselves 

 followed much the same line of cleavage. Although he accepts to 

 a large extent, with regui'd to his families, the system proposed 

 by Dendy [1892 BJ, Bidder makes certain rearrangements whicli 

 do not appear to be altogether satisfactory. He does good 

 service, however, in indicating for the first time the relation- 

 ship of Carter's Clathrina tripodifera, for which he proposes 

 the genus Dendya, to HaeckeUs Leiccaltis clalhria {^^Hetero- 

 pegma nodus-gordii Polejaeff"). In the same paper he discusses 

 the position of the crystalline optic axis of the radiate spicule 

 systems, and endeavours to assign taxonomic value to this 

 character also, but whatever may be the theoretical value of his 

 conclusions, which have since been accepted by Minchin [1909], 

 we cannot consider that such a character is of any practical use 

 to the systematist. 



In 1908 Jenkin erected two new families, the Cbijjhoridae and 

 StaurorrhaphidjB, supposed to be difterentiated by the presence of 

 what he considered to be a new type of spicule, the " chiactine," 

 from all previously recognised families. The peculia,rity of these 

 spicules was believed to consist in the orientation of the various 

 i-ays both in relation to one another and to the other parts of the 

 skeleton, and a special method of development was suggested for 

 them. Finally, in 1909, one of us (Row) still further elaborated 

 tlie " Chiact Theory," as it was called, and pi'oposed yet another 

 family, the Grantillidfe, in which more primitive, but similar, 

 " prochiacts " were supposed to be present, and which was mfide 

 by him the starting-point from which the Heteropiid^e were 

 supposed to have been derived. As we shall show later, however, 

 we do not now think that the spicules in question are more than 

 very slight modifications of ordinary types, and we have abandoned 

 all three families. 



