I. On the segmental excretory organs of certain fresh-water ostracods

Abstract

The origin of the duct of the segmental excretory organs of Crustacea is of critical importance in the consideration of the relationships of these organs to each other and to the similar organs in other Arthropoda. Up till now, it has been by no means certain what that origin is, or even whether the ducts have one common origin throughout the group. In a study of the development of Estheria it has been suggested by the author (1924, p. 422) that the divergences of opinion on this point may be due to the fact that segmental excretory organs are not completely homologous throughout the group. The end-sacs may be, and probably are, homologous, but not the ducts. Burian and Muth (1921, p. 642) place these glands in two groups according to the constitution of their efferent ducts. In the first group the duct is built up of a large number of cells, and the lumen is intercellular; in the second it consists of a few cells only, and the lumen is intracellular. The efferent duct of the maxillary gland of Estheria is the first type and it is a true cœlomiduct, that is to say, it is completely mesodermal in origin.