24 



ZOOLOGY 



flagellata, with no collar round the base of the flagellum; and 



the Choanojlagellaia, in 

 which the protoplasm is 

 produced into a collar which 

 surrounds the anterior end, 

 from the middle of this the 

 single large flagellum takes 

 its origin. Godosiga(Evg.lSi) 

 is a colonial form of this kind, 

 composed of long branching 

 stalks, the end of each branch 

 bearing an individual. 

 These collared flagellates 

 have a striking resemblance 

 to the collar cells lining 

 the flagellate chambers in a 

 sponge ; and a genus, Pro- 

 terospongia (Fig. 19), dis- 

 covered by Saville Kent, in 

 which the individuals of 

 the colony are sunk in a 

 jelly, lends some support 

 to the view that Sponges 

 may have originated from 

 colonies of Choanoflagel- 

 lata. In this genus the 

 individuals near the sur- 

 face are of the typical 

 form ; but certain wander- 

 ing amoeboid cells have 

 sunk into the central jelly, 

 and some of these have 

 become spherical, and then 

 divided up into micro- 

 gonidia, in a manner recall- 

 ing the formation of sper- 

 matozoa in a Sponge. 

 Most Flagellata live in fresh water ; some are marine, and 



some parasitic, living in the alimentary canal or blood of 



FlQ. 18. — A branch of Co(io- 

 siga cymosa, Sav. Kent. 



1. The stalk. 



2. Protoplasmic cell body, 



showing nucleus and 

 granular protoplasm. 

 Collar. 

 4. Single flagellum. 



