On the Embryology of the Isopod Irona1

Although Rathke (1834), Dohrn (1867), van Beneden (1869), and Roule (1889, 1890, 1891, 1894, 1896) have studied the embryology of Isopoda, the first detailed account and the one that is ordinarily quoted in text-books is that of Bobretzsky (1874) on Oniscus murarius. This work is informative in a general way, though the details of segmentation and germ layer formation are not accurate. Bullar's (1878) work on the parasitic isopods was largely influenced by the generalizations of Bobretzsky. Nusbaum (1891a, 1898) and McMurrich (1892, 1895) have contributed considerably to our knowledge of segmentation and post-mandibular growth in isopods but their accounts of the different fates of the germ layers left several problems of embryology unsolved. Goodrich's (1939) studies on Porcellio and Armadillidium were confined mainly to the origin and fate of the endoderm elements. Manton's (1928) paper on the development of Hemimysis serves as a landmark in the history of Crustacean embryology.