[Rudimentary stages of the extremities of Scelotes gronovii (Daudin) embryos, a South African Scincidea reptile].

The development of the limbs has been studied in 15 embryos of Scelotes gronovii, found in 8 ovoviviparous females collected at Saldanha Bay, in South Africa, Cape Province. This study leads to the following constatations: In all the young embryos of this species, their appears anlagen of anterior and of posterior limb-buds. The primordia of forelimb-buds retrogress early and disappear, whereas the primordia of hind limb-buds transform into rudimentary limbs which persist in adult. Histological study of the anlagen of fore limb buds establish that 7 somites (S6 to S12, S1 being the first post-otic somite) send ventral processes in the mesoblast of the anlage. These processes follow a sinuous pathway in the limb-bud, and are bent towards the basal cell layer of the somatopleural mesoderm. On the apical part of the limb-bud lie a wholly rudimentary epiblastic ridge, which disappears early. On the apical part of the hind limb-bud an ectodermic ridge is present, well differentiated which transforms soon in an apical fold; and the anlage of the hind limb produced a short conical appendage with short femur, tibia and fibula and one terminal finger. A comparison was made of the main steps of the development of the limbs in three species of Scelotes with rudimentary limbs. Scelotes inornatus, Scelotes brevipes and Scelotes gronovii. In these three species the ectodermal apical ridge of the fore limb-buds is rudimentary or incompletely differentiated; it never transforms into an ectodermal fold and its retrogresses rapidly; and in these species an early arrest of development and an involution of the primordia of the limb-buds occurs. These fact corroborate the anterior observations made on embryos of Anguis fragilis and of Ophisaurus apodus and they strengthen the interpretation postulating that the spontaneous retrogression of the apical ridge is an essential factor in the morphogenetic events involved in the arrest of development of the limb bud in the snake-like Reptiles.