Conlon, Rita Judge2012-09-062012-09-0619401940b1477925https://hdl.handle.net/2144/4123Thesis (M.A.)--Boston University, 1940As a large Metazoa developed, osmosis and streaming of protoplasm had to be replaced by a more efficient maintenance system. A complex arrangement of invaginations would provide sufficient absorptive area, vut no advance is possible with such a system. Circulation is an effective means of distributing materials, but a large body with an entire surface cannot absorb enough material to maintain itself. By combining systems of invaginations and circulation, however, the poor features of each system are eliminated.en-USBased on investigation of the BU Libraries' staff, this work is free of known copyright restrictionsThesis/Dissertation