132 



THE RADIOLARIA 



circles, which may be compared to the equatorial, the two circum- 

 polar, and the two tropical circles of the globe (Miiller's law). In 

 a few cases two radii mark the vertical axis, and the other eighteen 

 are disposed in three circles an equatorial one, and the other two 

 respectively 45 above and below it (Brandt's law); whilst in the 

 apparently primitive Astrolophidae the spines vary in number and 



Fio. 18. 



Acanthonia tetracopa in its two extreme phases of expansion and contraction, one half of the 

 animal being drawn in each case. The relation of the myonemes to the ectoplasm, and their 

 insertion into sheaths around the radial spines, is also seen (cf. Fig. 11). The full number (20) 

 of spines is not indicated. (After Schewiakoff.) x 170. 



possess no regular arrangement beyond their radial disposition. 

 This loose order is repeated in the early development of the Acan- 

 thoniidae. The young of this family possess ten loose rods arranged 

 crosswise, which subsequently become divided at the centre of 

 the capsule into the typical twenty radii. In the Acanthochias- 

 midae the distal portion of each radius gives off tangential processes- 

 which unite with those of adjoining spines and so form a perforated 



