iv] THE SECOND GRADE 95 



whole, the body which we are accustomed to think of 

 as constituting the basis of the only real individuality 

 in an animal. These cells, however, are scarcely 

 inconvenienced. After a short period of shock during 

 which collar and flagellum are withdrawn, they begin 

 joining up one with another, forming irregular solid 

 lumps which, gradually hollowing their central parts, 

 are soon transformed into hollow perfect spheres, 

 their walls a single sheet of cells, and the flagella, 

 now active, beating on the outside. The general 

 resemblance to Volvox (p. 104) is striking, and is 

 made more remarkable by the existence of a group 

 of Protozoa the collared flagellates or Choano- 

 flagellata whose essential structure is identical with 

 that of the collar-cells ; if one of these artificially- 

 produced spheres were found in nature, it would 

 certainly be taken for a colony of Choano-flagellates. 

 Many of these spheres were kept alive for over a 

 month, and there is little doubt that if the right food 

 were found, they could exist indefinitely, though what 

 would happen with the multiplication of the cells 

 and the consequent growth of the spheres it is hard 

 to prophesy. This remains to be tried ; but the 

 facts as they stand are interesting enough. For 

 untold generations no collared cells of a sponge have 

 ever existed except as a subordinate part of a 

 whole sponge-body ; and yet, if artificially freed 

 from that "harmonious constellation," they can act 



