The Development of the Embryo and Membranes of the Humpback Whale, Megaptera nodosa (Bonnaterre)

Abstract

The material consists of 20 embryos (5-30 mm) and two foetuses (63 mm and 90 mm) collected at whaling stations on Moreton and Norfolk Islands (latitude 27º 11'S. and 29º 5' S. respectively) during late August, September, and early October in 1952-53-54 and 1956. The consecutive series permitted the study of membrane formation and organogenesis.

Younger embryos are found in grooves between the folds of endometrium in a constant site in that uterine horn associated with the ovary containing the recent corpus luteum.

Older embryos and the early foetus are adapted to lie freely in the uterine fluid, and are devoid of any mechanism for apposition or attachment to the endometrium.

Variation in the sequence of the association of the components of the umbilical cord provides suspensory structures for the amnion and yolk sac, and for the embryo a bifid ligament, retained in the early foetus for attachment of the foetal membranes.

In the younger foetus the allantoic duct drains the nephric secretion into the uterine cavity. In the older foetus chorionic villi are present. The bifid suspensory ligament forms the major part of the distal region of the umbilical cord. The allantoic duct is reunited with the allantoic sac.

Amniogenesis is by folding. During the embryonic period the chorio-amniotic connection forms a suspensory ligament. The yolk sac, attached by a novel ligament to the amnion, is large and functional in the embryo. In the foetus vascular splanchnopleure is present in a tubular form.

A rete system develops in the embryo.