SARCODINA 83 



genus at their junction with the calymma, are contractile and are used 

 in the regulation of the diameter of the body. 



Lithocircus (Fig. 37). (Suborder Nassellaria.) A siliceous skeleton 

 in the form of a ring, bearing spines. Yellow cells extracapsular. 



Aulactinium (Fig. 69 B). (Suborder Phaeodaria.) A skeleton of 

 hollow, radial, compound, siliceous spicules, not meeting in the 

 centre; nuclei two; central capsule with three oscula, one of which is 

 surrounded by a mass of coloured granules (the phaeodium^ from 

 which the suborder is named). Like the rest of the Phaeodaria this is 

 a deep-sea form and does not possess yellow cells. 



Order HELIOZOA 



Sarcodina, generally of floating habit and freshwater habitat ; without 

 shell or central capsule; sometimes with siliceous skeleton; with 

 spherical bodies; typical axopodia; and usually a highly vacuolated 

 outer layer of protoplasm. 



The locomotion of members of this group, in the ordinary phase, 

 is effected as rolling, due to contraction of successive pseudopodia 

 in contact with the ground so that the body is pulled over. The 

 pseudopodia usually show streaming of granules. When they bend, 

 which they do to enclose prey which has adhered to one of them, their 

 axial filaments are temporarily absorbed at the bend. Protoplasm 

 from the pseudopodia then surrounds the prey and streams with it 

 inward to the endoplasm, where a food vacuole is secreted around it. 



Contractile vacuoles are present. 



Asexual reproduction is usually by binary fission (or plasmotomy in 

 multinucleate forms), sometimes by budding. Sexual processes have 

 only been thoroughly investigated in Actinophrys and Actinosphaerium, 

 where they take the form of autogamy (see below). 



Dimorpha (Fig. 70), one of the Helioflagellata, a small group of 

 organisms which is usually appended to the Heliozoa, bears somewhat 

 the same relation to that order that Naegleria bears to the Amoebina. 

 It has a biflagellate and a heliozoan phase, and can pass from one to 

 the other. In the latter it retains the flagella, whose filaments share 

 a common basal granule with those of the axopodia, and has no 

 vacuolated layer or protecting case. In fresh waters. 



Actinophrys (Figs. 71, 72). Unprotected ; with one nucleus, against 

 which the central filaments of the axopodia end; no skeleton. Auto- 

 gamy (or more correctly paedogamy^) takes place as follows: the 

 pseudopodia are withdrawn and a jelly cyst formed. Binary fission 

 now takes place, so that two individuals lie side by side in the cyst. 



^ Paedogamy is a kind of autogamy in which not only the nucleus but 

 also its cytoplasm divides and reunites. 



