12 BRITISH PRUSHWATER HULIOZOA. 



the two centi"OSomes, the process is then completed in 

 the normal way, and when the plasma finally divides 

 two uni-nnclear individuals are the resiilt. 



Simple division in the same species without mitosis 

 of the nucleus takes the form either of binary 

 fission or of simple or multiple gemmation without 

 any division of the centrosome ; during the process 

 the pseudopodia are not withdrawn and the nucleus 

 divides directly one or more times, one of the resultant 

 nuclei remains in the parent, the others travel to the 

 periphery and each emei'ges with a bud which is 

 covered with spicules derived from the parent and is 

 uni-nucleai'. After the buds are separated they may 

 enter into a resting-stage prior to becoming mature 

 individuals, or they may divide one or more times before 

 developing pseudopodia ; again, a bud may become 

 amoeboid and leave its investment of spicules, or it 

 may by simple division give rise to several amoeboid 

 individuals, or again it may develop two flagella and 

 become what is termed a " flagellula," retaining this 

 form for a day or two before it becomes amoeboid ; 

 these amoeboid forms eventually all become spheroidal 

 and- secrete a spicular investment; the nucleus then 

 gives rise to the centrosome, after which the radial 

 axes of the pseudopodia are formed. 



The formation of swarm-spores- has been observed 

 in the genera Glathridinu, Acanthocj/stis, and Acfiiio- 

 phri/fi* These spores are isogametes. 



Collection and Examination. 



Heliozoa are not uncommon in freshwater lakes, 

 ponds, pools, and ditches ; they can usually be found 

 creeping on the bottom if the water is not muddy, 

 or attached to algae and aquatic plants; plankton 

 gatherings taken in a finely-meshed net are also likely 

 to yield thorn. 



To collect Heliozoa from the bottom, if the water 



* Cienkowsld ; Schaudinn ; Penard. 



