Credit: Viz' Shonen Jump's Hollow Classification

After a human dies, they become one of two kinds of spirits:

1) Whole -- A normal spirit that will pass on to the Soul Society peacefully. (Image on the right is an example. Notice the chain attached to his chest.)

2) Hollow -- A spirit whose intense emotions warp their soul, turning them into an angry mass of rage. They attack the living and the dead and devour their souls.

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Menos are Hollows that consume other Hollows and become stronger in the Process. There are 3 classes:

1) Gillians: The lowest class. A Hollow formed from hundreds of ravenous Hollows. They are gigantic but slow and have the intelligence of wild animals. (Image on the left.)

2) Adjuchas -- Occasionally a personality of a Hollow transcends the others in a Gillian and becomes dominant. It can then consume other Gillians and become an Adjucha. Adjuchas are highly intelligent and dangerous.

3) Vasto Lordes - Some Adjuchas have the ability to evolve and become Vasto Lordes. They are the strongest among the Menos.

Shown above are some examples of Hollow forms

To be continued...