IN NATURE (vol. xvii. p. 284) is a notice of a work by Dr. Palmen, of Helsingfors, on the morphology of the tracheal system. From the wording of the notice it appears as if the views of Dr. Palmen as to the origin of tracheae from skinglands, and as to the importance of Peripatus as an ancestral form of the Tracheata, were new to science. I was, to the best of my belief, the first to discover that Peripatus was provided with tracheae; and in a paper on the structure and development of Peripatus capensis, published in the Phil. Trans. for 1874, I discussed the question of the origin of tracheae, and put forward exactly similar views to those cited in your notice. These views have been adopted by Prof. Gegenbaur in his new edition of his “Grundriss der Vergleichenden Anatomie” (1878), in so far at least as that Peripatus is placed in a separate division of the Arthropoda, “the Protracheata”. Haeckel, following Gegenbaur, supposed his Protracheata to have been provided with tracheal gills, but the diffuse arrangement of the tracheae in Peripatus led me to conclude that the ancestral tracheata were terrestrial, and not aquatic, in habit, and that tracheal gills were comparatively late developments.