The development of Daphnia magna

Abstract

A general account is given of the development of Daphnia magna from the egg to the mature adult. A review of previous work reveals that authors have concentrated on the early development, neglecting the later development. An adequate technique has been developed.An account of the development based on living material gives a detailed series of stages. A summary of the present state of knowledge of the physiological aspects of development is included. The development of the parthenogenetic egg is described. The early development includes a superficial cleavage and gastrulation by immigration. The mesenteron develops from a solid rod of cells in the ventral part of the egg, and acquires a central cavity which never contains yolk. The yolk cells develop from the blastoderm. The mesoderm develops a single small pair of coelomic cavities, and the heart develops from a compact group of cells. The history of the dorsal organ is described. The development of the ephippial egg resembles that of the parthenogenetic egg except in some features related to the smaller and more even sized nature of the yolk globules.Daphnia magna hatches from the brood pouch of the mother as an immature adult. The account of the anatomy of the adult is a confirmation and extension of previous work, including histology and indicating function. The muscles of the mesenteron are striated, and the heart wall contains anincomplete longitudinal, as well as a circular, layer of muscles. A suggestion is made for a new interpretation of the cells of the branchial sacs. The results obtained and the importance of a large quantity of yolk are discussed.