"what type of digestion involves the gastric mill? do rats accomplish that type of digestion in their stomachs? "

Since they don't have teeth, crawfish have a gastric factory that aides in absorption in the stomach. The factory is like teeth however are in the stomach. Rats don't have the kind of processing in their stomach since they have teeth.

The answer to this question would be: False

Gastric mill is an organ located inside the stomach that was used to grind the food so it would be smaller and easier to digest. This organ found in the animal that doesn't have teeth, so they just swallow their food whole.
Rats don't have gastric mill because it was not needed. Rat has teeth and can cut their food into many smaller part that easy to digest.

Crossing over creates new combinations of genes in the gametes that are not found in either parent contributing to genetic diversity