Eukaryotic organisms have a variable number of chromosomes in their body cells. This number is species-specific.

Here's why:

* Species-Specific: The number of chromosomes is determined by the organism's evolutionary history and is a characteristic of the species.

* Diploid: Most eukaryotic organisms are diploid, meaning they have two sets of chromosomes (one set from each parent).

* Examples:

* Humans: 46 chromosomes (23 pairs)

* Fruit flies: 8 chromosomes (4 pairs)

* Dogs: 78 chromosomes (39 pairs)

It's important to note that the number of chromosomes doesn't directly relate to an organism's complexity.