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ROYAL SOCIETY OF CANADA 



and flattening the spicules are usually much displaced. Within these, 

 secondary' and smaller squares are marked out by smaller spicules. 

 Judging by the length of the rays of the larger spicules, the larger squares 

 would bo about 4 mm. in diametei-, Avhilst the smallest do not exceed 



I / 



Fio. 3. — Protospongia tetranemn. Primary, secondary and 

 tertiary cruciform spicules, x 5, 



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

 raei-ely by the animal matter, and not by a silicious cement. The osculum 

 is protected by 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 be nearly cylindrical. 



From the base of the sponge, four slendei-, elongated, filiform rods 

 project. They ai'e approximately cylindrical, pointed at both ends, very 

 slender, and from 50 to 70 mm, in length. Their proximal ends are 

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

 specimens they are seen to approach and cross each other in the middle, 

 and then to diverge, fina' again approaching and forming a loop with 

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







Fig. i.—Protosponffia tetranema. Osculum enlarged 



and surrounded by minute spicules. Fiu. 5. — Anchor! ng-rods. 



been found that there can be no doubt as to its true natui-e, though in a 

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

 in this case, however, they show their cui-ved ends (Fig. 5). 



