MATERIALS FOR A MONOGRAPH OP THE ASOONS. 525 



monaxons. My observations, so far as they go, liave by no 

 means dispelled this suspicion. 



Lendenfeld employed the presence or absence of monaxon 

 spicules to classify Ascons. If the term "monaxon spicule" 

 be employed without further qualification, it represents a 

 character which, if used for systematic purposes, yields, to my 

 mind, a very artificial classification. But I think it extremely 

 probable that primary monaxons will be found restricted to 

 the Leucosolenijdse, where they are the first spicules 

 formed, and that in Clathrinidae, where the triradiate 

 systems appear first, the monaxons are secondary. This is, 

 however, at present a pure speculation. I hope at some future 

 time to be in a position either to prove or to demolish these 

 views. 



Appendix. — A few points in connection with the formation 

 of the spicules or with their cells seem to call for special 

 notice before leaving the subject. 



(1) The Triradiates of Clathrina clathrus.— In 1892 

 ([3] p. 183) I described the spicules of this form as having on 

 their rays sometimes one cell, sometimes two, and sometimes 

 a cell with two nuclei close together. As this is rather a 

 different state of things from anything I have found in the 

 species investigated in this paper, I examined the point again, 

 and find my description perfectly correct. Looking now at a 

 series of drawings made by me at that time with the aid of the 

 camera lucida, I have come to the conclusion that the apparent 

 anomaly is due to the frequent persistence of the apical forma- 

 tive cell on the fully formed spicule rays of this species. When, 

 as is frequently the case, there are two nuclei in a single cell, 

 adherent to the tip of the spicule, I believe this to be brought 

 about by the basal formative cell having travelled to the apex 

 of the spicule ray, and there fused with the persistent apical 

 cell. 



That the apical cell should persist in this way is rather 

 unusual, but may perhaps be connected with the cylindrical 

 form of the rays, which in this species terminate abruptly 



