[Footnote 25: Leuckart, in his great work, "Die Menschlichen Parasiten," p. 700, after the analogy of Hirudo, which develops a primitive streak late in larval life, ventures to consider the first indications of the germ of Nemertes in its larval, Pilidium form as a primitive streak. He also suggests that the development of the later larval forms of the Echinoderms is the same in kind. Moreover, nearly twenty years ago (1854) Zaddach, a German naturalist, contended that the worms are closely allied in their mode of development to the insects and crustaceans. He compares the mode of development of a leech (Clepsine) and certain bristle-bearing worms (Saenuris, Lumbricatus and Uaxes); and we may now from Kowalensky's researches (1871) add the common earth worm (Lumbricus), in which there is no such metamorphosis as in the sea Nereids, to that of insects; the mode of formation of the primitive band in the leeches and earth worms being much like that of insects. This confirms the view of Leuckart and Ganin, who both seem to have overlooked Zaddach's remarks. Moreover, the rings of the harder bodied worms, as Zaddach says, contain chitine, as in the insects. Zaddach also enters into farther details, which in his opinion ally the worms nearer to the insects than many naturalists at his time were disposed to allow. The singular Echinoderes has some remarkable Arthropod characters.] [Footnote 26: Vergleichende Anatomie, 2te Auflage, 1870, p. 437. I should, however, here add that I am told by Mr. Putnam that some fishes which have no swim-bladder, are surface-swimmers, and _vice versa_.] [Footnote 27: Reported In "Nature" for Nov. 9, 1871.] [Footnote 28: The Embryology of Chrysopa, and its bearings on the Classification of the Neuroptera, "American Naturalist," vol. v. Sept., 1871.] [Footnote 29: "It is my opinion that the 'incomplete metamorphosis' of the Orthoptera is the primitive one, _inherited_ from the original parents of all insects, and the 'complete metamorphosis' of the Coleoptera, Diptera, etc., a subsequently acquired one." _Fuer Darwin_, English Trans., p. 121.] CHAPTER XIV. INSECT CALENDAR.