100 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
(fig. 1089), which is closely allied to the common Bell-Animalcule 
(Vorticella), a non-colonial form. And another colonial form 
(Codosiga), represented in the same figure, also has solitary 
relatives. In cases where a number of units are associated 
together it is clearly advantageous that there should be a “ divi- 
sion of labour”, on similar principles to those which have increased 
Fig. 1089.—Colonial Animalcules, enlarged to various scales. a, Efistylis; c, c, small individuals conjugating with 
large ones; d, d, d, d, individuals undergoing fission. 3, Codosiga. c, Proterospongia. 
the output and improved the quality of manufactured articles. 
There are certain colonial Animalcules which exhibit an early 
stage in division of “physiological” labour. Of this an excellent 
example has already been given (see vol. iii, p. 333) in Volvox, 
where some members of the colony become specialized in con- 
nection with propagation by means of eggs. As another instance 
we may take Proterospongia (fig. 1089), which consists of nu- 
merous individuals imbedded in a gelatinous substance. Some 
of these are charged with the duty of securing food for the colony, 
and the projecting end of each such individual is surrounded by a 
