LATTICE WORKERS, OR POLYCYSTINA. 107 



lattice shell is excreted simultaneously. In others 

 they are developed from separate lattice plates, 

 deposited in succession. 



" The skeleton in the great majority is armed with 

 radial spines, which are of great importance in the 

 development of their general form, and of their vital 

 functions. The number, arrangement, and dispo- 

 sition of the spines is usually the determining factor 

 in the general form of the skeleton. Physiologically 

 they discharge distinct functions, as organs of pro- 

 tection and support ; they act also, like the tentacles 

 of the lower animals, as prehensile organs, since their 

 points, lateral branches, barbed hooks, &c., serve to 

 hold fast nutritive materials. In general, main 

 spines and accessory spines may be distinguished : 

 the former are of pre-eminent importance in deter- 

 mining the figure of the skeleton, the latter are 

 merely appendicular organs." l Accessory spines 

 may include all those processes which have no in- 

 fluence in the determination of the form of the 

 skeleton as a whole. They are developed in the 

 utmost variety, sometimes as hairs or bristles, some- 

 times as thorns or clubs, either straight or curved, 

 smooth or barbed, sometimes standing vertically 

 upon the shell, or directed towards the centre, some- 

 times obliquely, or rising at a definite angle. 



1 Challenger : " Report on the Radiolaria," p. Ixxxix. 



