ORIGIN OF THE METAZOA 



43 



-LI '.':/ I I U. 



Fig. 14. Colonial ciliates. Anoplophrya is colonial only in that the 



cells formed by asexual division often remain attached in the form 



of a chain. (From Borradaile and Potts.) 



contract individually. Zoothamnion is of interest in that it shows 

 considerable variation in the structure of its units, the colony 

 showing division of labour (Faure-Fremiet (1930); Summers 

 (1938)). 



Colonies are found in the cnidosporidian Sporozoa, the spores 

 showing well-marked differentiation into cnidocysts each with its 

 own nucleus, a spore nucleus and a spore case nucleus (Fig. 15). 

 Whether it is justifiable to regard these reproductive units as 



Fig. 15. Colonial sporozoa. The spores of the Cnidosporidia have 

 a complex structure, (a) Shows the adult trophozoite and it will 

 be seen to resemble the trophozoite of other sporozoans such as 

 Monocystis. (b) Spore case together with the undischarged thread 

 cells, (c) Spore case with discharged thread cells. 



(a) Sinuolenea. From Grasse after Davis. 



(b) Myxobolus. From Grasse. 



(c) Chloromyxum. From Grasse after Kudo. 



