110 ANIMAL INDIVIDUALITY [OH. 



breaking off from its stalk, it divides up into a large 

 number of little cells each of which develops two 

 flagella, takes on the form characteristic of the 

 free-swimming Peridineae, and is off to infest new 

 hosts. Here, it will be seen, the same cell devotes 

 itself at one period to nutrition and at another to 

 dispersal. 



In Blastodinium mycetoides (Fig. 9, b), these two 

 functions are carried on by different structural units : 

 the full-fed cell does not break off from the stalk that 

 nourishes it, but divides transversely into two halves 

 which become separated by a membrane. The one 

 that is no longer attached to the stalk at once begins 

 dividing up to form little flagellates, while the other 

 goes on feeding, grows to full size again, and cuts off 

 a second reproductive cell. 



Now imagine the reproductive cells to remain 

 organically connected with the stalk-cell and to be 

 nourished by it for some time after they have been 

 divided off, and you have in essentials a simple species 

 of Haplozoon (Fig. 9, c e). 



The Catenata and Volvox are thus similar in 

 being multicellular organisms with unified function 

 and with division of labour among their parts ; but 

 their origin is very different. 



In the making of Volvox, community-life mere 

 aggregation came first, division of labour last. In 

 Haplozoon's history, division of labour existed before 



