THE REPRODUCTION OF RADIOLARIA. "75 



Thus the individual skeleton is reduced and even lost. In 

 tiphcvrozoum, each individual is surrounded by a lattice-work of loose 

 spicules of the elegant six-spin ed form shown at fig. E, PI. XII. In 

 other species, it is absent (Collozoum). Sometimes these colonies 

 reach considerable size. Collozoum attains a full inch in length. 

 tij)/tcvrozoum is smaller and usually globular, perhaps iVin. in length, 

 but sausage-shaped colonies of J-in. long are fairly common. 200 to 

 300 individuals are frequently associated together, being arranged 

 peripherally in a hollow gelatinous sphere, arising from the general 

 coalescence of the gelatinous outer extra-capsular layer (calymna) 

 of each member. This layer being common to all, it follows that the 

 protoplasmic network of the surface, and the radiating pseudopodia 

 are also common, ensuring the even distribution of nutriment. Thus 

 in a Radiolarian colony such as Sphcvrozoum, we have each individual 

 with its own separate central capsule, its own separate sarcomatrix 

 and its own protecting lattice work of spicules ; but calymna, 

 sarcoplegma and pseudopodia are shared in common by the colony. 



If we examine carefully the sarcomatrix of Spkcerozoum, we see 

 a varying number of deeply stained bodies lying irregularly spread in 

 the sarcomatrix of each individual. Some have many, some have 

 few, and it may happen that we may see some possessing none. In 

 life, these bodies are yellowish, and it is inferred that they are 

 parasitic, or, more probably, symbiotic algas. It appears that these 

 yellow cells can live equally well, and even multiply, when separated 

 from their host. Each has been found to possess a distinct cell-wall 

 of cellulose, a nucleus, two colouring matters, one of which is 

 chlorophyll, and lastly, to complete the vegetal characters, the power 

 of forming starch. They are present in nearly all species, though 

 some individuals are occasionally free from them. In the present 

 species, some individuals are crowded with them, while others have 

 comparatively few. These cells multiply within the host by the 

 division of their protoplasm into four parts which secrete separate 

 cell-walls and then break through the parent membrane. If removed 

 from the host, they eventually become biflagellate, i.e. provided with 

 two whip-like threads of protoplasm, flagella, their locomotive organs. 

 Some have referred them to a distinct genus of algae, while others 

 believe them to be the swarm spores of several species of olive- 

 green seaweeds (Fucus, &c.) It is probable that they assist in the 

 respiration and nutrition of their hosts, by contributing oxygen 

 and starch. 



The reproduction of the Radiolaria is most intricate, and 

 betokens the high development to which the group has attained. If 

 we take a fully adult colony of Spkcerozoum, we find that the 



