Exocrine secretions are discharged onto some external or internal body surface through a(n) .

The correct answer is "duct".

Explanation:

The structures at which substances are secreted in the body are known as ducts. For instance, the liver and the pancreas act as exocrine glands liberating bile and pancreatic juice, respectively. These exocrine glands secrete the substances from the gastrointestinal tract through a series of ducts. The ducts could be branched or unbranched, depending on the location at which the exocrine secretion takes place.

when the displaced particles are perpendicular to the direction the wave travels, is called a transverse wave, whereas in longitudinal wave the displace practices are parallel to the direction of the wave.

in the given image:

first image shows - longitudinal wave

second image shows - transverse wave

third image shows - longitudinal wave

fourth image shows - longitudinal wave