The Sarcodina 205 



Around the nucleus, there is a hyaline layer in which the axonemes end. 

 In the Acanthocystis-type (Fig. 5. 2, A), the vacuolated zone is lacking 

 and the body is covered with a test composed of skeletal elements em- 

 bedded in a capsule. Some such covering is found in the majority of 

 Heliozoa. Beneath the relatively thin ectoplasm there is a thick granular 

 zone containing one or more contractile vacuoles, food vacuoles, and 

 other inclusions. Within the granular layer, a zone of clear cytoplasm 

 contains the "central granule" and a nucleus. The central granule, in 

 which the axonemes converge, resembles a centrosome in its behavior 

 dining mitosis (Fig. 5. 2, D). However, Stern (139), on the basis of multi- 

 nucleate and other abnormal stages seen in cultures, has argued that the 

 central granule does not really function as a centrosome. 



Fig. 5. 3. A-D. Ingestion of a fiagellate by Acanthocystis aculeata, succes- 

 sive stages; xl215 (after Stern). E. Formation of a food vacuole outside the 

 test in Hedriocystis pellucida; xl050 (after Hoogenraad). F. A large lobo- 

 podium, in addition to axopodia, in Raphidocystis infestans; x8I5 (after 

 VVctzcl). G. Cytostome-like structure, with food vacuole at the base of the 

 "gullet," in Actinosphaerium eichorni; x34 (after Okada). H. A ciliate (Para- 

 mecium) attacked by a group of Raphidocystis infestans; xl28 (after Wetzel). 

 I. A ciliate completely surrounded by such a group; stained preparation; x238 

 (after Wetzel). 



