Simple systems that lack gonads use undifferentiated tissue to form gametes. External fertilization: eggs shed by the female = fertilized by sperm in outside environment. Internal fertilization: sperm are deposited in/near female reproductive tract. Requires behavioral interactions + compatible copulatory organs (sexual) Some eggs have: calcium & protein-containing shells. Some have: retain the embryo and develop inside the female. Some simple systems lack gonads = gametes form from undifferentiated tissue. Accessory glands (secrete products needed for sperm movement) The 2 seminal vesicles contribute ~60% of total volume of semen. Composed of sperm + secretions from 3 sets of accessory glands. Prostate gland: secretes its products directly into urethra through small ducts. This neutralizes acidic urine remaining in urethra. Female external rep. organs: clitoris + 2 sets of labia. Chambers that carry gametes + house embryo & fetus. Small sacs of epithelial tissue secrete milk. All 4 products of meiosis develop into sperm, while 1 out of 4 becomes an egg.