3io THE TANGANYIKA PROBLEM. 



SPONGILLA MOOREI (R. Evans). 



This sponge grows on the shells of various mollusca, and partially covers them as 

 a crust. The upper surface is raised into lobes or mound-like elevations, which in 

 no case are more than half an inch above the general surface, and which are usually 

 no more than an eighth of an inch above the shallow depressions which separate 

 them. The surface texture of the preserved sponge is somewhat woolly in appear- 

 ance, though this is probably the result of the broken condition of the dermal mem- 

 brane, for it has been observed that some of the fragments preserved in Flemming's 

 fluid are smooth, and the spicules of the skeleton, though supporting the dermal 

 membrane, do not in the natural condition penetrate it. 



An osculum is situated at the tip of each of the lobes or mound-like elevations of 

 the surface of the sponge. This opening measures about an eighth of an inch in 

 diameter, and underlying it there is a fairly large gastral cavity. The dermal pores 

 are small, as usual, and are situated on the flanks of the lobes as well as in the 

 intermediate depressions. 



(2) The Skeleton. — In treating of the skeleton or the supporting part of the 

 sponge, first, the spicules will be described ; secondly, the arrangement of the 

 spicules to form fibres, and of the fibres at large to form the skeleton, and thirdly, 

 the spongin which binds the fibres together. 



(A) The Spicules. — In order to facilitate description, the spicules will be 

 divided into three classes, the ordinary division into "megascleres," and " micro- 

 scleres " being intentionally avoided, because it is, to say the least, doubtful 

 whether the small, smooth spicules are microscleres or young megascleres. 



The three classes of spicules are : — 



(a) Diactinal monaxons, which taper to a sharp point, either gradually (amphioxea) 

 or more rapidly (amphitornota), and are without swellings on their shaft. The 

 former are always straight, the latter curved (Fig. I — a.). 



(/8) Similar straight amphioxea or curved amphitornota, with distinct swellings 

 on the shaft (Fig. 1 — d.). 



(7) Irregular systems formed by the fusion of spicules belonging to class a. 

 (Fig. 1). " 



(a) The straight amphioxea taper gradually into a sharp-pointed end (Fig. 1 — b.), 

 while the curved amphitornota, which are far more numerous, taper much more 

 abruptly into a similar point (Fig. 1 — c). Both the straight amphioxea and the 

 curved amphitornota are highly variable in thickness, and exhibit all stages of 

 development. The axial thread is of even thickness throughout its whole length in 

 all these spicules. 



(j3) In addition to being slightly more slender than the spicules already described, 

 the main feature of these spicules is the presence of a number of swellings which 

 varies from one to five. As a rule they are situated symmetrically with regard to 

 the middle point. of the spicule ; that is, if there is only one swelling it is situated 

 at that point, but if there are two they are placed one on each side of that point, and 

 at equal distance from it ; and similarly the symmetry is maintained when there are 

 three, four or five swellings. The absence of the symmetrical arrangement, as seen 



