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ROYAL SOCIETY OF CANADA 



and fliittoniiin tlu' spicuk'S are usually nnich displaced. Within thewc, 

 st'rondarv and smaller S((uares are marked out l»y smaller spicules, 

 Judi^ini^ Ity the loiiifth of the rays of the la rger spicules, the larger squares 

 would he ahout 4 mm. m diameter, whilst the smallest do not exceed 



Fn;. '.i.—Protospotij/ia tetranrma. Priiniiry, secondary and 

 tertiary cruciform spicules, x 5. 



1 mm. The rays of the individual spicules seem to have heen united 

 merely hy the animal matter, and not by a silicious cement. The osculum 

 is protected hy defensive spines (Fig. 4). and in young specimens these 

 are often very numerous. The rays of the larger spicules are conical, 

 gradually tapering from the central node to the pointed extremity ; 

 whilst the rays of the smaller spicules appear to he nearly- cylindrical. 



From the base of the sponge, four slender, elongated, filiform rods 

 pi'oject. They are api)ro.\imately cylindrical, pointed at both ends, very 

 slender, and from 50 to TO mm. in length. Their proximal ends are 

 inserted apparently in the basal part only of the .sponge. In perfect 

 s])ecimens they are seen to approach and cross each other in the middle, 

 and then to diverge, finally again approaching and forming a loop with 

 a minute central point. So many examples of this structure have now 





sf 



'%^t^4# 



Fig. A.—Protosponffia tctrancma. Osculum enlarged . 



and surrounded l)y minute spicules. Fm. o.— Anchoring-rods. 



been found that there can bo no doulit as to its true mitui-e, though in a 

 few instances the loop has broken asunder, leaving the rods free. Kven 

 in this case, however, the}' show their curveil emls (Fig. 5). 



