192 



PROTOZOA. 



Forms with skeleton and those without are distinguished. To the first 

 belong Clathrulinaelegans, with a spherical lattice-work skeleton supported 

 on a stalk (fig. 121). Acanthocystis turfacea, skeleton of radial, branching 

 needles. To the forms without skeleton belong first Actinosphcerium 

 eichhorni, as large as a pin-head, milk-white, protoplasm foamy from the 

 numerous fluid vacuoles, the different sizes of which markedly distinguish 

 cortical from medullary proportions. The contractile vacuoles are in the 

 cortex, the nuclei in the medulla. In encystment the foamy appearance 

 and most of the nuclei are lost, and a cyst is formed with numerous uni- 

 nucleate daughter cysts. Each daughter cyst divides into secondary cysts 

 which, after the formation of polar globules, fuse^ (fertilization) and 

 produce germ spheres. From these then escape, after a long rest, the 

 young Actinosphceria. The reproduction of Actinophrys sol, a smaller 

 form, is essentially similar. 



Order IV. Radiolaria. 



The Radiolaria, the most beautiful and most highly organ- 

 ized of the Rhizopoda, strongly recall, in their appearance, the 



? 



/**: 



X 





FIG. 123. Thalassicolla pelagica. In the centre the nucleus with coiled nucleolus, 

 around it the central capsule with oil globules; still outside the extracapsular 

 soft body with vacuoles (extracapsular alveoli), yellow cells (black) and pseu- 

 dopodia. 



Heliozoa. They are spherical, only rarely by flattening converted 

 into disks, or by unequal growth into conical or lobular shapes. 



