INTEODUCTION. 



REPRODUC'LTOISr. 



Solitary individuals in the Heliozoa may multiply 

 by binary fission or budding, during which processes 

 the nucleus may divide either directly or hj karyo- 

 kinesis ; multiple budding or gemmation may take 

 place similai-ly, and in some species this gives rise to 

 temporary or permanent colonies. 



The buds may grow directly into mature individuals 

 or may form small flagellate or amoeboid zoospores 

 which are known as " swarm-spores." Syngamy or 

 the conjugation of two individuals has been accurately 

 observed . in very few instances ; the process in the 

 case of Actinophrys is described below (p. 10). 



Karyokinesis in the Heliozoa is of a normal type, 

 the nuclear membrane being ruptured and either 

 persisting or being absorbed. 



Centrosomes may or may not be formed during 

 division, depending on the species concerned and on 

 the nature of the process which varies very consider- 

 ably even in different members of the same order. 



As previously stated there are three groups into 

 which the Heliozoa may be divided according to their 

 nuclear characteristics, viz. : 



(1) Multi-nuclear. 



(2) Nucleus placed centrally. 



(3) Nucleus placed eccentrically. 



Each of these groups* presents certain differences 

 in the processes of nuclear division which may be 

 briefly summarised. 



The first group is represented only by the genus 

 Actinospheerium among the freshwater species. In 

 A. p-lchliornii, which may possess some hundreds of 

 nuclei, karyogamy has been observed and may be 

 described as follows : — A single individual withdraws 

 its pseudopodia, exhibits amoeboid movements, ejects 

 food-particles, and forms a membranous " mother " 

 cyst, the peripheral vacuoles disappear and the nuclei 

 ai'e much reduced in number either by absorption or 



