96 TOILERS IN THE SEA. 



appears to be variable, usually one, but sometimes 

 more. 



The fate of the flagellate zoospores is uncertain, as 

 all attempts to rear the swarming zoospores has 

 failed, but, from analogy, the hypothesis seems to be 

 fully justified, that they are converted into an inter- 

 mediate actinophrys stage, in which the body becomes 

 spherical, with fine pseudopodia protruding all round, 

 whilst the nucleus assumes a central position. 



What has been termed the sphcerastrum stage is 

 believed to succeed. This stage arises from the 

 actinophrys stage by the excretion of an external 

 jelly-veil. In this condition the young Radiolarian 

 is a simple cell, with pseudopodia radiating on all 

 sides, its body consisting of three concentric spheres, 

 viz., the central nucleus, the protoplasmic body proper 

 and the surrounding jelly-veil. When a firm mem- 

 brane is developed between the last two spheres, 

 this stage passes over to the next, or actissa stage. 

 Probably in all Radiolaria the sphcerastrum stage de- 

 velops immediately into the typical actissa stage, by 

 the formation of a firm membrane between the pro- 

 toplasmic body and its jelly-veil. Thus arrives the 

 simplest form of Radiolarian organisation, with the 

 central body differentiated into an inner capsule and 

 outer capsule, by means of the intervening membrane. 



The general course of individual development 

 begins with the formation of zoospores in the central 



