272 A. EARLAND ON RADIOLARIA. 



for some time the zoospore comes to rest and passes into what 

 we may call the Actinophrys stage. It probably assumes by 

 contraction a spherical shape, loses its flagellum, and develops 

 radial pseiidopodia all over its surface, the nucleus assuming a 

 central position. In this condition it would practically be an 

 Actinophrys, 



The Actinophrys stage is probably connected with Actissa by an 

 intermediate form, which may be regarded as a simple skeleton- 

 less Heliozoon with a " jelly-veil," such as Sjyhcerastritm (in the 

 solitary condition) and Heteroiylivys. The young Radiolarian in 

 this second or Sph?erastrum stage becomes a simple cell with 

 pseudopodia radiating on all sides. Its body consists of three 

 concentric spheres — the central nucleus, the protoplasmic body 

 proper, and the surrounding calymma or jelly-veil. 



The formation of a firm membrane, the capsule membrane, 

 between the sarcode body and the jelly-veil completes the trans- 

 formation from a Sphserastrum to a true Eadiolarian in its 

 simplest form, Actissa. Thus arises the central capsule, the 

 characteristic feature of the Radiolaria, which is wanting in their 

 nearest allies, the Heliozoa. Actissa is not only the simplest 

 Radiolarian known to us, but is also probably the true prototype 

 of the whole class, as it is the simplest form under which the 

 Radiolarian organism can be conceived. 



Although reproduction by spore formation is probably the 

 normal habit with all Radiolaria, there are certain families, notably 

 the social Spumellaria ( Poly cytt aria), in which the organism in- 

 creases by spontaneous cell division. The central nucleus separates 

 (by direct nuclear division) into two halves, the central capsule 

 follows suit, becoming constricted between the two nuclei, each of 

 which finally becomes enclosed in one of the two new capsules. 

 As this process does not involve the extra-capsulum at all, we 

 arrive eventually at a stage in which a number of sister cells, 

 which have arisen by repeated division of the parent nucleus and 

 capsule, are enclosed in a common rapidly-growing calymma, 

 forming a true coenobium or colony. 



Reproduction by gemmation or budding has been observed 

 in the Radiolaria, but so far only in the social Radiolarians 

 (Polycyttaria), where it appears to be widely distributed. The 

 gemmules or capsular buds are developed on the surface of young 

 central capsules which have not yet secreted a membrane. After 



