348 Mr. It. Kirkpatrick on 



suggested, however, to emphasize the fact that the distal end 

 of the clavula or scopula is wholly devoid of end-spine3 or 

 distal appendages. 



The forms of the clavulse and scoptdfe pressnt the same 

 kind of contrast as that existing between amphidisks and 

 hexasters. The distinction is purely a morphological one, 

 however, for both clavulae and scopulae are found together in 

 Claviscopulia intermedia, F. E. Sch. In the case of the 

 amphidisks and hexasters the distinction is significant from 

 the phylogenetic as well as the morphological point of view. 

 Amphidisks and hexasters are astral, and clavulas and scopulse 

 are holactine spicules. The latter belong to the subgroup of 

 tnicromonactins, a category which should be placed below the 

 microhexactins in the morphological scheme ('Annals,' I. c. 



p. 209). 



The root-tuft spicules of Hyolonema are mega-monactins 

 with centrodisks. Here again there are no end-spines at the 

 true distal end of the spicule. 



The remarkable uncinates with their highly specialized 

 lateral spines are diactins, which should, I think, in spite of 

 their large size, be classed asmicroscleres. Accordingly they 

 would come under the category of microdiactins. 



I take this opportunity of making a correction. In a 

 paper " On the Phylogeny of the Amphidiscophora " 

 (' Annals/ Nov. 1909, p. 479) I wrote :— " What appears to 

 be a second character" — in Amphidiscophora — "is the 

 existence of genuine microhexactins, which do not exist, so 

 far as I have observed, in the Hexasterophora. (The small 

 hexactins forming ] art of the framework in Dictyonine 

 sponges are not here regarded as microhexactins)." 



I have row found in certain Dictyonine sponges {Earete 

 sewpert, F. E. Sch., &:.) microhexactins which could not be 

 regarded as loose spicules which would later be welded so as 

 to form part of the dictyonal framework. Accordingly the 

 name Microhexactinophora could not be used as an alternative 

 name to Amphidiscophora. Microhexactins seem to have 

 entirely disappeared, however, fiom many Lyssacine sponges, 

 in which the seeming hexactins are hexasters. 



The hexasters in Dictyonine sponges are frequently of a 

 primitive type, i. e. the actines are relatively long and the 

 end-spines often little more than short thorn-like prickles; in 

 more highly evolved hexasters the actines tend to become 

 shorter and the end-spines longer, more curved, and tipped 

 with toothed disks. 



The total disappearance of microhexactins from so many 

 of the Hexfisterophoi-a is surprising in view of the fact that 



