A. EARLAND ON RADIOLARIA. 271 



legion the central capsule in its growth more or less envelopes 

 the primary perigenous skeleton, which then lies partially 

 within it. 



Haeckel recognises twelve different types of skeleton formation, 

 some peculiar to a single legion or even part of a legion, while 

 others occur in several legions. The descriptions of these types 

 and their distribution in the legions are too technical for 

 introduction here. 



The skeletons of most Kadiolaria are armed with radial spines, 

 which are of importance both morphologically and physio- 

 logically. Their number and arrangement are a determining 

 factor as regards the general form of the skeleton, and they also 

 discharge the functions of organs of protection and support. 



Life History. 



Owing to the difficulty of direct observation, the life history of 

 the Kadiolaria is incompletely known. From what has been 

 actually observed, coupled with deductions from observations 

 made in respect to their nearest allies, the Heliozoa, the life 

 history would appear to be somewhat of this nature. After 

 maturation, the nucleus of the central capsule breaks up into a 

 great number of small nuclei, each of which becomes a zoospore 

 by surrounding itself with a small particle of the endoplasm ; it 

 generally absorbs one or several fat granules, and sometimes a 

 small crystal. Each of these zoospores is furnished with one or 

 more long vibratile flagella, and commences its movements while 

 still enclosed in the central capsule. The extra-capsulum takes 

 no part in the development of the species. Presently the central 

 capsule ruptures and the spores escape, the parent Radiolarian 

 then dying. The zoospores, which at this stage of the life history 

 resemble a flagellate infusorian of the simplest class, such as 

 Astasia, are ovoid or subcylindrical, averaging -005 mm. in 

 diameter, and swim freely by means of their flagella. 



All attempts to cultivate these zoospores have failed, and a wide 

 gap ensues between the swarm spore and Actissa, the simplest 

 Eadiolarian adult form known. This gap can only be bridged 

 by assuming that the young Eadiolarian passes through several 

 Hehozoon-stages, following one on another. Thus from analogy 

 with the Heliozoa it may be assumed that after swimming freely 



