BRITISH FRESHWATER HELIOZOA. 



exerted at will. The instantaneous appearance and 

 disappearance of oils on the flowing- plasma of Amoeba 

 }>ilosa Cash and Mastigina setosa Frenzel seems to be 

 a similar phenomenon. In two species, Acanthocystis 

 rnh^Ua Penard and Raphidocystis stellata Penard, the 

 pseudopodial axes are formed by the silicious spines 

 which invest their envelopes and are consequently 

 permanent, only the plasma with which they are 

 coated being retractile. 



The Heliozoa use their pseudopodia as instruments 

 of progression, their extremities attaching themselves 

 to whatever support they happen to be on and then 

 drawing the animal forward with a rolling motion, 

 the various pseudopodia coming into action in 

 succession ; in furtherance of this action those about 

 to come into use may be slightly elongated and bent 

 forward; by these means a fairly rapid rolling 

 progression may be attained. There is also evidence 

 that they may be used for free-swimming movements. 

 They are brought into action for the capture of food 

 in which operation they may curve inwards and their 

 extremities sometimes coalesce. With the above 

 exceptions they do not ordinarily anastomose except 

 in the species Raphidiophri/s viritUs, Actinosph&rium 

 arachnoideum and the arenus Clafltrnlina. Amoeboid 



O 



pseudopodia are sometimes displayed by mutilated 

 or detached portions of some species, and they may 

 f also appear just previous to encystment as in Actino- 

 xfiltx'i-iniu, but with the above exceptions other than 

 rigid pseudopodia are quite abnormal in. mature forms ; 

 during the development of swarm-spores amoeboid 

 forms occur. 



The pseudopodia of the Heliozoa are not analogous 

 to those of the Rhizopoda, and under the description 

 of Dimorpha mutans will be found reasons for thinking 

 that they may possibly be derived from modified 

 flagella. 



