BY R. VON LENDENFELD, PH.D. 907 



6. The slender Dermal acei'ate spicules are of the same length, 

 as the former, but only 0"003 thick. They are rare, and situated 

 in the tufts between the others. 



7. The acerate spicules of the Oscular frills are similar to those 

 in the chamber tufts, but larger. 



The upright ones are slightly curved, the convex side towards 

 the axis ; they are pointed at both ends, and measure 1"5 — 2 

 X 0-015— 0-02 mm. 



The lower frill is composed of spicules similar to the slender 

 acerate ones of the tufts ; these are slightly curved, the convexity 

 towards the basis of the Sponge, and measure 0*5 — 1 x 0'004. 



DEVELOPMENT. 



I have traced the postembryonal development, or metamor- 

 phosis, as it may be termed, of Homoderma. 



The young Sponge is cylindrical, with short acerate spicules 

 distributed equally all over the surface, and presents, therefore, 

 the same outer appearance as the Spongorhiza, 



There is a slight trace of an Oscular frill visible. 



It grows in size without changing its shape, but developes the 

 two frills of the Osculum. All this time the inner surface is 

 perfectly simple. Our Sponge is an Ascon. 



With the development of the first excresences of the Entoderm, 

 when in the centre of the Sponge, a few chambers make their 

 appearnce ; tufts of spicules also appear on the surface 



Move chambers and tufts are developed ; the Sponge grows, and 

 the Oscular frills attain the large size we find in the adult. The 

 small, equally distributed spines of the young, ax'e then only found 

 in those parts of the Sponge which do not contain ciliated 

 chambers. 



The Sponge has attained the structure of the full-grown adult 

 when it is 2 mm. high. 



Colour : Light yellow. 



Locality : South Coast of Australia, Port Phillip, Victoria. 



