Morphology of the reproductive tract in a lizard exhibiting incipient viviparity (Sphenomorphus fragilis) and its implications for the evolution of the reptilian placenta.

摘要: The morphology of the female reproductive tract and corpus luteum is examined in Sphenomorphus fragilis, a lizard from lowland regions New Guinea exhibiting incipient viviparity. Females oviposit eggs that hatch either immediately or within few hours. Corpora lutea form ovulated follicles decrease diameter as embryonic development progresses. oviduct vitellogenic females sparsely populated with well developed uterine glands containing secretory granules. are covered relatively thin shell (10 μm thick) composed an inner boundary layer proteinacous fibers. secreted complete by early neurulation. Shell does not change throughout remainder utero incubation period. A vascularized uterus chorioallantoic membrane provide simple placentation. These findings suggest reduction thickness associated evolution placenta due to number delay inhibition shelling process per se. This hypothesis further suggests selective forces favoring gland loss act on during recruitment which occurs prior ovulation pregnant female. © 1992 Wiley-Liss, Inc.