506 Mr. R. Kirkpatrick on 



sections, considered that the collar cells had a " Leucosolenid " 

 rather than a u Clathrinid " aspect ; as he has pointed out, the 

 flagellum arises from the terminally situated nucleus in Leuco- 

 soietria, but in Clathrina fr.om a granule separated a long way 

 from the basally situated nucleus. It maybe mentioned here, 

 too, that the sagittal spicules of Minchinella suggest Leuco- 

 solenid affinities. The dimensions of the collar cells are as 

 follows : — total height 19 fi ; collar 145 /a high ; body of cell 

 4*5 /a; diameter of I ase 5'28 fi. The cells vary in size, the 

 figured ones (PI. XIII. fig. 8) being the largest. 



In the spaces between the collar cells are the pore cells 

 with funnel-shaped apertures, the narrow opening of the 

 funnel being, as usual, external. 



Skeleton. — On both surfaces of the sponge there rs an ecto- 

 somal layer of more or less fusiform spined microxeas, longer 

 and more slender on the oscular than on the poral surface. 

 These spicules form a thick outer coat on the poral and 

 oscular chimneys, and are described along with the other 

 spicules of those structures. The skeleton of the poral and 

 oscular chimneys is constructed of triradiates, quadriradiates, 

 and monaxons. As a rule, there are several layers of tri- 

 radiates, with the odd ray passing downwards and with the 

 paired lays encircling the tube; the quadriradiates have the 

 gastral ray projecting into the lumen of the chimneys, and 

 the monaxons are arranged as an external pile with the axes 

 vertical or oblique to the long axis of the tube ; there is a 

 fringe of bristle-like monaxons round the poral orifice. At 

 the bases of the poral and oscular chimneys three-rayed and 

 four-rayed spicules with thick spined rays become cemented 

 together, but are not yet completely enveloped by that 

 material. Lastly, there is the firm framework of quadri- 

 radiates completely enveloped in cement. 



Poral Spicules.— (1) Triradiates (PI. XIV. fig. 4), with 

 thick, slightly curved, gradually tapering, nit her blunt-pointed 

 rays ; unpaired ray longer than the paired and curving back- 

 wards a little from the facial plane; angle between the paired 

 rays 150°. Unpaired ray 156 fi long, 9"5 fi thick at base ; 

 paired ray 87 //. long. 



(2) Quadriradiates (PI. XIV. figs. 1, 2, 3), of the same 

 general character as (1), but with longer basal rays; gastral 

 ray 17 /a long, sharp-pointed, curved upwards. A different 

 kind (PI. XIV. fig. 3) has nearly equal basal rays, the odd 

 one being spined, and a much longer gastral ray ; these were 

 found at the base of the soft part of the pore-chimney and near 

 the outer wall of the tube, so that the gastral ray traversed 

 nearly the whole thickness of the wall. 



