Ongoing classes continue throughout the year, but are divided into two-month series. You are welcome to join these classes at any time, either on a series or drop-in basis. If you join after the series has begun, the series fee will be prorated. Pre-registration is not required for ongoing classes. Fees for ongoing classes are:   1 1/2 and 2 hour classes Series basis, $13 Drop-in, $15 1 hour classes Series basis, $9 Drop-in, $11   Special classes that meet for one or two months only, such as Introduction to Yoga, Yoga for Back Care, and Zen Meditation, are available on a series basis only. Pre-registration is essential for these classes. Special Classes 8 Weeks, $112 4 weeks, $56