n] 



RADIOLARIA 



27 



bottle keeps the gas dissolved) and all the shells composed of 

 chalky matter are dissolved, only the flinty skeletons being left. 

 The bottom mud here entirely changes its character and is called 

 Radiolarian ooze. When Radiolaria reproduce the chromatin of the 

 nucleus breaks up into a chromidium from which secondary nuclei 

 are formed. Round these nuclei spore-like masses of protoplasm 

 aggregate themselves and these escape as isospores, each of which 

 has two vibratile filaments or flagella (see below). At other times 

 some only of the chromatin of the primary nucleus breaks up into 

 a chromidium, the rest divides into larger pieces and thus 

 anisospores, that is spores of two sizes, large and small, are formed, 

 each of which possesses two flagella but one of these encircles the 

 protoplasm like a belt. It is probable that these spores must 



FIG. 6. Heliosphera inermisxSSO. From Biitschli. 

 1. Skeleton. 2. Central capsule. 3. Nucleus. 



conjugate to form a zygote before they can develop ; in a word 

 that the isospores are asexual germs but that the anisospores are 

 gametes. 



The next group of Protozoa to be considered is a very remark- 

 able one, including the largest forms known. The 

 so-called "Flowers of Tan" (Mycetozoa) are brightly 

 coloured patches, which may be seen on the surface of the oak-bark 

 used in tan-pits. Similar patches may be seen on old tree stumps 

 and on the surface of beanstalks which have been wet for a con- 

 siderable time. These patches under the microscope are seen to 

 resemble enormous Amoebae with thin branching pseudopodia, 

 which are apt to join one another to form networks, although these 



Mycetozoa. 



