Species of Donatia (Tethya). 13 



raised above the general surface. On Sept. 5 they were 

 projecting slightly. On Sept. 6 many of these elevations 

 formed the ends of buds whose connexion with the parent 

 sponge gradually narrowed to a slender stalk. Spines 

 appeared from the sides and ends of the buds. On Sept. 7 

 the first bud dropped off. 



If a fresh specimen of average size, i. e. about 15 mm. in 

 diameter, be cut in two, it is seen to have a .well-defined 

 cortex 1*5 mm. thick, consisting of a thin tough inner layer 

 of white fibrous material and a thick fleshy outer layer orange 

 in colour. The choanosome is dark yellow at the centre and 

 bright green at the periphery, the two colours merging into 

 each other at two-thirds the distance from the. centre to the 

 periphery. Numerous large glistening white fibres rim from 

 the centre radially in all directions; in the cortex one of them 

 spreads out at the base of each conule. 



For the study of spicules preparations were made as 

 follows: — From a freshly collected sponge a small piece was 

 cut in any desired region, placed upon a microscope-slide, and 

 covered with a few drops of KOH or NaOH solution ; the 

 slide was then held with forceps over a low alcohol flame at 

 a sufficient distance so that the fluid would not quite boil 

 but would become hot enough to soften the tissue. The 

 alkali was then washed off with water from a pipette, and a 

 cover-glass placed over the softened tissue and pressed down 

 flat with a needle. This procedure was carried out with 

 fragments taken at various points along the radius of a large 

 number of specimens. 



The sponge contains four kinds of spicules : — (1) Mega- 

 scleres, typically strongyloxeas, but with the ecactine often 

 rounded, 1*0 to 1*4 mm. long by 13 to lb' /j, in diameter, with 

 smaller forms down to 0*3G mm. by 6 fi. (2) Spherasters, 

 ranging from 30 to 50 /a in diameter, with straight, abruptly 

 pointed, oxeate actines, very abundant in the cortex, espe- 

 cially in its deeper portion, and at the periphery of the 

 choanosome, but exceedingly rare elsewhere. (3) (Jxyasters, 

 28 to 35 fi in diameter, with slender rays, usually six in 

 number, straight and uubranched, though occasionally curved 

 or bent and rarely branched. These are found occasionally 

 in the outer half of the cortex and are fairly abundant in the 

 inner half, while throughout the entire choanosome they are 

 very numerous, by far the most abundant microsclere. 

 (4) Chiasters — 6'6 to 13*3 //. in diameter, and tylote — form 

 a dense sheet at the periphery of the cortex, and are abundant 

 through the remainder of the cortex and outer choanosome, 

 but exceedingly rare in the deeper parts of the choanosome. 



