148 



PfiOP. ST. GEOBOE MIVAllT 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 Pliysematium * and the compound 

 form SpJicsrozoum italicum f) , as short, separate, solid, needle-like, 

 but more or less curved spicula. They are placed tangentially 

 around the capsule. Some of those of Physematium 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 ^. Those 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. 



JN^ext comes the compound genus Bhaphidozoum, round the cap- 

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

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

 plex of those before mentioned as occurring in Physematnim) ; 

 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 Sphcerozoum 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. punctatmn **. 



"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. (Aftei* Ehrenberg.) 



* See ' Eadiolarien,' pi. iii. fig. 9. 



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



II L. c. pi. xxxii. fig. 11. 



** L. c. pi. xxxiii. fig. 7. 



t L. c. pi. xxxiii. fig. 2. 

 § L. c. pi. iii. fig. ] 3. 

 ^ L. c. pi. xxxiii. fig. G. 



