THE SPONGES. 97 



radial bundles. The rhabdome of the anatriaene is coiled in a loose 

 spiral round that of a dichotriaene, the cladome of the former lying just 

 below the cladome of the latter. 



Radical anatriaenes, Fig. 11, Plate 12, occur in considerable number 

 in the smaller specimen ; none found in the larger specimen. Rhabdome 

 always broken, 20 fx thick above ; cladi, 85-250 fi long ; cladome deep. 

 The cladi and rhabdome are somewhat stouter than in the somal spicules. 

 The cladi vary a good deal in curvature as well as in length. In some 

 spicules they are markedly incurved as in the specimen figured, in others 

 nearly straight or only very slightly curved. The spicules occur in the 

 spicular core of the rootlets, 



S. Oxea. a. The common large form measures 9 mm. x 50 /u, to about 

 one-half this size ; median enlargement with axial cross sometimes present, 



especially in the smaller sizes ; spicule tapering evenly to each end. 



The spicules are abundantly scattered in the parenchyma, where they 

 cross at all angles, sometimes running side by side so as to form bundles 

 of two or a few. Tliey also accompany the rhabdomes of the dichotriaenes, 

 aiding in the formation of the obliquely radial skeletal bundles. They are 

 also found singly or in bundles of two or three, lying tangentially in the 

 dermal membrane on both surfaces. 



b. Very slender oxeas, 6 mm. x 12-15 fx to one-half this size, form 

 part of the obliquely radial skeletal bundles. The spicule is cylindrical, 

 tapering gradually at each end to a fine point, and is curved usually two 

 or three times in a wave-like manner. These oxeas are twined round the 

 larger spicules of the bundles. 



Similar oxeas, reaching a greater length, 9 mm., occur in the rootlets, 

 where together with the other longitudinally arranged spicules they form 

 a sort of core. 



c. Small oxeas about 1 mm. x 10 /a project from both upper and lower 

 surfaces in considerable number, forming in places a pretty thick furze. 

 The spicules project obliquely or about radially. A few similar spicules 

 occur scattered in the parenchyma. Others lie tangentially in the dermal 

 membrane. 



Microsckrcs. 



4- Spirasters, Figs. 1 a-e, Plate 13; abundant in the dermal mem- 

 brane, pore membranes, and choanosome ; somewhat less abundant in the 

 ectosome ; spicules of the several regions not distinguishable. 



13 



