148 



PEOF. ST. GEORGE MI FART ON 



solid or, more rarely, hollow ; and in the latter case they are tra- 

 versed by the sarcode. 



The circumferential system appears, in its most rudimentary 

 condition (in the simple form Physematiiim * and the compound 

 form Sphcerozoumitalicumf), as short, separate, solid, needle-like, 

 but more or less curved spicula. They are placed tangentially 

 around the capsule. Some of those of Vliysematium exhibit the 

 next degree of complication in that they give off at intervals and 

 at right angles short pointed processes. 



A step further is shown in the exceedingly long and delicate, but 

 hollow spicules oi Aulacantlia% and Thalassoplaneta §. Tho!>e of 

 the former genus are so numerous and relatively minute as to 

 form an investing layer towards the outside of the extracapsular 

 sarcode with its large alveoli. Those of the latter genus are 

 of enormously greater size relatively. 



Next comes the compound genus Rhaphidozoum, round the cap- 

 sules of which we find simple spicula, like those of SpJicerozoum 

 italicum, but with short secondary processes (like the more com- 

 plex of those before mentioned as occurring in Fhysematium) ; 

 and, in addition, other spicula, each formed of four such needles 

 radiating from a common point ||. 



Another step in advance, as regards complexity, is by the com- 

 pound species SpJicerozoum ovo-di-mare % where each spiculum is 

 in the form of a short rod which subdivides at each end into three 

 radiating processes, and these may be provided with secondary 

 processes, as in S. punctatum **. 



"We have seen that the needle-like spicula of Aulacantha are so 

 numerous as to form a disconnected investment and network of 



Fig. 5. 



CornuteUa scalaris. (After Ehrenberg.) 



* See ' Eadiolarien,' pi. iii. fig. 9. t L. c. pi. xxxiii. fig. 2. 



X L. c. pi. ii. fig. 1, and pi. iv. figs. 4 & 5. ^ L. c. pi. iii. fig. 13. 



II L. c. pi. xxxii. fig. 11. IF ^- C' pl- xxxiii. fig. 0. 

 L. c. pl. xxxiii. fig. 7. 



