14 INVERTEBRATE MORPHOLOGY. 



cialized for reproductive purposes, while the rest take but 

 little part in this process. Such a colony presents indica- 

 tions of a passage towards a higher grade of individuality, 

 some of the various cell-individuals merging to a certain ex- 

 tent their individualities in that of the entire colony, aud 

 becoming somewhat dependent for existence on the coopera- 

 tion of their fellows. This dependence, however, never 

 reaches a high degree of development in the Protozoa and is 

 for the most part entirely absent. It is in this respect that 

 colonial Protozoa differ from the higher organisms, but the 

 difference is one of degree, not of kind. 



Four well-marked classes may be distinguished among 

 the Protozoa : 



I. 01. Ilhizopoda. 

 I.I. 01. Sporozoa. 



III. 01. Flagellata. 



IV. 01. Infusoria. 



I. CLASS RHIZOPODA. 



The simplest Rkizopods present an approach to the least 

 complicated condition under which protoplasm is known to 

 us. They are simply small masses of protoplasm, more or 

 less granular towards the centre, clearer towards the periph- 



cv 



FlG. 3. Amoeba proteuK (after GRUBER). 

 cv = contractile vacuole. n = nucleus. ps = pseudopodium. 



ery, and continually alter their shape by pushing out lobe- 

 or thread-like processes known as pseudopodia (Fig. 3, ^>,v). 



