376 



The Unity of the Organism 



spheridae. We will now look a little further into the devel- 

 opment of portions of these animals. 



Hacker's hypothesis of "directing centers" in some of 

 these animals is particularly interesting for us. What the 

 general purport of the hypothesis is can be readily under- 



FIGURE 22. AITLOSPHAERA (AFTER HAECKEfi). 



c.cap., central capsule. 



stood by the help of figures 22 and 23. The skeleton of the 

 genus here represented is a "lattice-sphere," in Hacker's 

 terminology, consisting of a network of tubes joining one 

 another in such a way that six pieces unite at each nodal 

 point. This scheme makes each mesh of the net a triangle. 

 A radial piece or spine bearing short branches arises from 

 each nodal point. The lumen of the tubes contains a gela- 



