The question asks in which part the process of gaseous exchange during respiration does not take place. Let's examine each option:

1. Skin of earthworms: Earthworms perform respiration through their skin. Their skin is moist and allows gases to pass through by diffusion. Hence, gaseous exchange takes place here.
2. Alveoli of humans: Alveoli are tiny sacs in the lungs of humans that play a critical role in gas exchange. Oxygen and carbon dioxide are exchanged between the alveolar air and the blood in the surrounding capillaries. Thus, gaseous exchange occurs here.
3. Gills of Pila: In aquatic animals like Pila (snails), gills are the primary respiratory organs where gaseous exchange with the surrounding water takes place. Therefore, gaseous exchange occurs here as well.
4. Bronchi of humans: The bronchi are large air passages in the lungs that lead from the trachea to the bronchioles. While they carry air to and from the lungs, the actual exchange of gases (oxygen and carbon dioxide) does not occur in the bronchi. This exchange primarily occurs in the alveoli.

Therefore, the correct answer is that gaseous exchange does not take place in the bronchi of humans.