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Abstract

COVER PHOTOGRAPH: Bony fin rays of the gonopodium, an intromittent organ, of the male swordtail fish, Xiphophorus helleri. Distal skeletal elements are differentiated into hook-like structures that facilitate efficient sperm transfer during internal fertilization. From Offen et al., Developmental Dynamics 238:1674–1687, 2009. © 2009 Wiley-Liss, Inc.