224 J. H. ORTON. 



Tiny specimens of C. normani were obtained by the writer from a 

 floating raft moored in Cawsand Bay, just outside Plymouth Sound. 

 These specimens measured about 13 and 14 mm. ; in fact, just the size 

 Norman wished for. These specimens were examined while living, and 

 sketches made from the living animal of all stages of gTowth of the bell- 

 shaped spicules. 



Subsequently a preparation was made of the skin of these animals 

 and a drawing of the spicules made in situ for Fig. 8, p. 225. This figure 

 shows the different stages of growth of the bell-shaped spicules and also 

 the degree in which these spicules are crowded in the surface of the skin. 

 The young of C. saxicola have been reared by the writer from the egg 

 to a size of about 5 mm., i.e. somewhat smaller than the tiny C. normani 

 mentioned above. In these no bell-shaped spicules developed, although 

 the body spicules were well formed. Specimens of all sizes of both species 

 have been obtained from dredgings, forming a parallel series from the 

 tiny ones mentioned above to the adults of sizes whose gonadial tubes 

 and other correlated characters have been described. The evidence for 

 the distinctness of these two forms is thus complete, whatever their 

 ultimate names may be decided to be. 



THE GROWTH-STAGES OF THE BELL-SHAPED SPICULES 

 OF C. NORMANI. 



The tiny specimens of C. normani mentioned above presented an 

 opportunity of following the development of the bell-shaped surface 

 spicules of this species. These spicules develop in four well-defined 

 stages. In the earliest stage they consist of a microscopic plate forked 

 at both ends (see Fig. 8 for this, as well as for the following stages). At 

 a later period of development each of the forked ends divides dichoto- 

 mously twice to give two succeeding well-marked stages. At the same 

 time the central portion of the spicule becomes wider and thicker, and 

 the grovv^ng arms arch outwards to form a hemisphere. At this stage 

 one branch of each of the last-formed bifurcations grows towards a 

 similar branch derived from the subdivision of the adjacent primitive 

 prong. These branches grow together, but frequently become slightly 

 forked again before fusing to form the rim of the spicule. The whole 

 spicule at this stage becomes thickened, and generally two branches of 

 the third order of division persist as projections at each of the four 

 corners and one in the middle of each side of the rim when the spicule is 

 fully formed. There are, however, sometimes variations from the general 

 course. Occasionally three or five original prongs may develop and a 



