German Model

Throughout the history Western Art, drawing the human figure from living models was considered the most useful tool in developing the skill draftsmanship. In the art school classroom setting, the purpose is to learn how to draw humans all different shapes, ages and ethnicities, so there are no real limitations on who the model can be. In some cases, the model may pose with various props, one or more other models, animals etc., against real or artificial background, in natural or artificial light and so on.
Models for life drawing classes are ten entirely nude, apart from visually non-obstructive personal items such as small jewelry and sometimes eyeglasses. In a job advertisement seeking nude models, this may be referred to as being "undraped" or "disrobed". (Alternatively, a cache-sexe may be worn. Eadward Muybridge's historic scientific studies the male and female form in motion, for example, has examples both usages.)
In Western countries, there is generally no objection to either sex posing nude for or drawing members the opposite sex. However, this was not always so in the past, particularly prior to the 20th century. In 1886 Thomas Eakins was famously dismissed from the Pennsylvania Academy Fine Art for removing the loincloth from a male model in a mixed classroom. Similarly, Victorian modesty required the female model to pose nude with her face draped (illustration). European arts academies did not allow women to study the nude at all until the end the nineteenth century. Up into the present day some rare art classes prefer male models to wear a jockstrap.
Policies vary regarding male models having an erection. Some instructors don't mind at all (especially with younger or inexperienced models), while others, including the Register Artists' Models (RAM) in the United Kingdom, consider this as cause for termination. In any case, it may be inconvenient for the artists, as the subject is not exactly the same as when the drawing session commenced.