284 ART. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



(liactiiis ; rough throughout, straight or slightly arched and some 

 with the central annular swelling or knobs. Total length, 286- 

 462/^ (on an average 380/^); thickness near the middle, 72-lle 

 /A Rarely the dermalia are stauractins or tauactins ; even pent- 

 actins and hexactins were met with amongst them during my 

 studies, though in quite a limited number of instances. 



I regard it important to mention that up to certain early 

 stages in the post-larval growth of the sponge, the dermalia may 

 be predominantly stauractins, not diactins as in all the larger 

 individuals. Thus, in the little sj^ecimen of PI. XXII., fig. 3, 

 as also in the still smaller one of only 3 mm. diameter, I find 

 stauractins more numerously represented among the dermalia than 

 diactins ; whereas, in the specimen of fig. 4, same plate, the two 

 forms of dermalia occur already in the inverse proportion. This 

 change in the predominant form of dermalia during the ontogeny 

 might well be regarded as the repetition of that which had taken 

 place during the phylogeny of the species. 



The ffastralia (PL XXII., fig. 13) are almost all liexactins 

 with rough, tci})ering and pointed rays. Exceptionally forms witli 

 a less number of rays and even diactins may occur as the gastralia. 

 The hexactins have distal and para tangential rays 120-220// in 

 length and 12-1 3 2 ,« in thickness at base ; the free proximal ray 

 may be twice as long as any other ray in the same spicule and 

 the microtubercles on it may be slightly more strongly developed 

 than tliose on the others. However, there not infrequently occur 

 such hexactins as have the proximal ray in no way specially 

 distinguished from the others. With their paratangentials the 

 hexactins form a continuous and regularly (|uadrate-meshed lace- 

 work. The sides of the meshes, 132-242 /^ long, are composed 



