The development of the Club-shaped Gland in Amphioxus

Abstract

ABSTRACT The club-shaped gland of the larva of Amphioxus has attracted much attention since its development was first studied by Kowalevsky in 1877 (4), who believed it to be derived from the first mesodermal segment. Hatschek, in his classical work published in 1881 (3), corrected this error, and described the origin of the gland from a transverse thickening of the endodermal wall of the gut on the right side opposite the mouth in the region of the first myotome. He states that, in the embryo of about 10 segments, this thickening extends dorsally up the right side, and ventrally on to the left side ; that it becomes folded, a groove being formed on its inner surface ; and that by the closing of the lips of the groove it finally becomes separated off as an elongated sac from the gut (‘Gegen das Ende der embryonalen Période erfolgt der Verschluss der Rinne und die Abschnürung dieser Bildung vom Darme ‘, p. 74). This sac on the right of the gut has a narrower prolongation to the left, which soon acquires an opening to the exterior just below the edge of the mouth (see Text-fig. 1). In the larva, then, the gland, whose wall is now formed of a layer of characteristic large cubical granular cells, opens by means of a duct partly ciliated and lined with flattened cells ; while at an earlier stage it is supposed to be a closed sac (‘der ganzen Lange nach zur Abschnürung gekommen ‘, p. 75).