224 DR. J- MURIE ON STEERE S SPONGE, 



render it likely that it extended over a great part of the branch, probably excepting the 

 summits of the whorled frills. Whether it extended over the stem it would be hazardous 

 affirmatively to assert, though the chances are it may have had a partial covering, basing 

 judgment upon what we know of other forms possessing a veil. Dr. Millar first drew my 

 attention to this structural point, and then we thought it only stretched over the large 

 orifices of the stem, a view we afterwards found erroneous. The significance of this 

 surface layer, both in a morphological and physiological point of view, I am inclined to 

 think is of considerable importance, but, as will be seen, it is not confined alone to this 

 form of hexactinellid sponge. 



Having run over the most noteworthy points of the external features of our specimen, 

 I come to the interior. In studying this, pieces were cut across and in the long direction 

 of the axis. The transverse sections of both stem and branches disclose not a hollow 

 cylinder as in Aphrocallistes and Aulodlctyon, a funnel-shaped or narrowed fusiform 

 cloacal cavity as in Rossella and Meyerina, nor yet quite such close areolae as in Bactylo- 

 calyx, but rather one may say a kind of compromise between the last two. While tubular, 

 these openings are unequal, the larger corresponding to the exterior oscular apertures, 

 the lesser to the pores aforementioned. The latter, angular and all sorts of shapes, are 

 bounded by the small cross and tangental spicules; the former, rounder or ovoid, are the 

 open passages between the larger-sized bundles of vertical and obliquely radiating spicules. 

 In the centre of the body of the stem the open tubular character is best marked towards 

 the periphery ; radii here are more visible, between which the short secondary spicula 

 intrude, while quite at the edge the frostwork of dermal sexradiate spicula encircles. 



The longitudinal median sections still further explain the preceding, and morever, in 

 some respects, agree with Meyerina, though in the general appearances and relative 

 thickness of the spicula an approach is made possibly nearer to Dactylocalyx. Longi- 

 tudinal fibrous-looking spicula appear to run up the entire length of the axis, but are in 

 fact a continuous repetition of stout sexradiate spicules, the cross bars being the short 

 arms. These median vertical pillars, moreover, most obviously branch off curvilinearly 

 towards the margins ; and it is evidently the production of these which gives rise to the 

 exterior whorls. Thus there is a certain plumular arrangement, the obliquely directed 

 spicules corresponding to the barbs, the smaller annectent spicules to the barbules, and 

 the dermal appanage of terminal sexradiates to the so-called extradivisional fluff of owl- 

 feathering. 



Microscopic Structure. — Before adverting to this it behoves me to mention the in- 

 valuable assistance derived from my friends Dr. John Millar and Mr. H. J. Carter. To 

 the former I am indebted for making my best illustrative microscopical specimens, and 

 also with liberal hand placing others of different genera at my disposal for comparison, 

 besides discussing points connected with the interpretation of structure. Mr. Carter's 

 labours and knowledge of Sponges, and especially of the group in question, are well 

 known and justly appreciated. When I add, then, that he has carefully examined portions 

 of the sponge, compared these with the figures in my Plates, and, moreover, measured the 

 spicula, drawing out a descriptive analysis of same for my use, it will be admitted I have 

 been amply helped and stimulated in investigating Professor Steere's specimen. In my 



