Spongillidaö. 241 



Skeleton:. Tlia skeleton consists of a close reticulation of single 

 spicules with very little trace of fasciculation; they are fastened together 

 by delicate veils of spongin where they meet. 



Spicules (PI. VI fig. 1): The skeleton-spicules are slender, bkmt, 

 nearly straight, covered somewhat sparsely and ahnostly uniformly with 

 sharp spines much less than half as long as the diameter of the shaft, to 

 which they stand out at right angles. Free microscleres exist in the form 

 of slender, nearly straight amphioxi bearing sharp or blunt spines that 

 stand out straight at right angles; they are much longer in the middle 

 region of the spicule than elsewhere but are never quite as long as its 

 transverse diameter. The gemmule-spicules as a rule resemble the 

 macroscleres in general form, but are rather more densely spined; they are 

 extremely variable in size and proportions and occasionally a little inflated 

 at the extremities. 



Gemmules (PI. VI, Fig. 2) : The gemmules adhere at the base of 

 the sponge in groups. Fach is enclosed in a dense cage about 0.04 mm 

 thick and composed of microscleres lying horizontally several spicules 

 abreast in a chitinous membrane; between this cage and the real gemmule 

 (inner capsule) there is a considerable gap; in the specimens examined 

 the roof of the cage is dehcient. The actual capsule has a relativ ely thick 

 chitinous coat (O.Ol mm thick) of a bright yeUow colour and is of a 

 somewhat irregulär shape ; there is possibly a single very minute foramon 

 at one side in a very short foraminal tubule, but the appearance may be 

 deceptive and I have not cut sections. On the surface ot the capsule lie a 

 few microscleres as a ride of somewhat distorted form and smaller than 

 those that compose the outer cage. 



Diameter of outer cage of gemmule ... 0.67 mm 



Diameter of inner capsule of gemmule . . . 0.27 „ 



Length of skeleton-spicule 0.16 „ 



Thickness of skeleton-spicule 0.014 „ 



Lenght of free microsclere 0.064 — 0.08 „ 



Thickness of free microsclere (shaft) .... 0.004 ,, 



Length of gemmule-spicule 0.104 (or less) „ 



Thickness of gemmule-spicule 0.012 



Locality: R. Zambesi near the Victoria Falls; W. Michaelsen, 

 18. August 1911. 



Type in the Hamburg Natural History Museum. 



Spongilla africana resembles S. indica Annandale in the structure of 

 its skeleton-spicules and its skeleton, but differs considerably therefrom in 



