There are two possible ways to save morphologies in neuroConstruct projects, both based on a mapping from the 
set of Java classes describing the cell internally in neuroConstruct:
-  XML based Java serialisation (*.java.xml files):  a mapping to an XML file of the classes. Note: not any part of NeuroML.
-  Serialised Java object form (*.java.ser files):   a serialised representation of the Java classes.

The second of these is quicker to load and save and the files are smaller. The first however can be opened (and edited!)
with a text editor. Change which format to use via Settings -> General Properties & Project Defaults/Project properties.

Cell morphologies are stored in the morphologies directory of the project home directory. *.bak files in that dir backup 
the previously stored morphology before a new one is saved (if a problem occurs saving a morphology, close the application, remove
the .bak from the name of the morphology file to use the previous structure of the cell when reloading the project).

Note that the cells aren't currently stored in neuroConstruct projects in NeuroML/MorphML format, since new functionality 
is usually added to the neuroConstruct Cell class before it is supported in the specifications.