REPORT ON THE MONAXONIDA. 



91 



Fig. 3. — Cladnrhiza mondi/onnis. Longi- 

 tudinal section of the head, showing the 

 arrangement of the slieleton ; a, axis of 

 stem and radial bands of fibres ; ca, capsule 

 of loosely disposed spicules, x 4. 



the centre of the head, radiate a large number of dense, stout spiculo-fibres (Fig. 3, o) ; 



each runs out to the surface of the sponge and is continued to the end of one of 



the conical processes already mentioned. Each conical 



process is thus supported by an axial fibre. (3) At 



about one-third of the distance between the surface and 



the centre of the head is a reticulate layer of megas- 



clera, which forms a kind of capsule (Fig. 3, ca), dividing 



the soft parts of the sponge into an inner and an outer 



portion. This capsule is, of course, pierced in numerous 



places by the stout radiating fibres already mentioned. 



Sjyicides. — (a) Megasclera ; long, slender, very 

 straight styli (PI. XXI. fig. 1), which may reach a length 

 of over 2 mm.; diameter about 0"05 mm. They are 

 broadest in the centre and taper gradually towards 

 each end, are flatly rounded at the base and hastately 

 pointed at the apex. (6) Microsciera ; (l) anisochelce 

 (PL XXI. fig. 19), of moderate size, length 0-063 mm. ; 

 these spicules have a slightly curved shaft, much expanded laterally towards the large 

 end ; the ends are of very unequal size and each has three sharp, prominent teeth. 

 (2) Large, very sharply pointed, contort .sigmata (PI. XXI. fig 15), measuring up to 

 0-35 by 0-0145 mm. 



The anisochelate spicules are especially abundant in the smaU conical processes, 

 forming a dense crust around the axial fibre, with their large ends directed outwards. 

 They are also very abundant in the tissues both inside and outside the " capsule." The 

 sigmata appear to be very much more abundant outside the " capsule " than inside it. 



Unfortunately this sponge was dry when the bladder was removed from its bottle, 

 and we have therefore been obliged to confine our observations to the arrangement of 

 the hard parts. It is a form of the very greatest interest, and aS"ords a good example 

 of radial symmetry in a Monaxonid sponge. It was a question with us whether or not 

 this species should form the type of a new genus, but we finally decided not, as no 

 essential changes are necessary to derive it from the more typical species, such as 

 Cladorhiza ahyssicola, Sars. Imagine an unbranched Cladorhiza ahyssicola in 

 which the points of attachment of the lateral pinnse to the axis come close together ; if 

 the pinnae are all of the same length the sponge will then have a globular form, and 

 little further change is needed to convert it into Cladorhiza moruliformis. The chief 

 difficulty is the capsule, and this is not an insuperable one. In some of the " Porcupine " 

 Cladorhiza' s (viz., Cladorhiza ahyssicola, var. corticocancellata, Carter), there is an 

 irregularly reticulate skeleton, chiefly placed at some distance beneath the surface, 

 between the main radial fibres, and if we imagine this to become concentrated into one 



