G. Wagner, Quart. Journ. Micr. Sci. xlviii. 1905, p. 589.
See p. [126].
Hydra pallida, Beardsley, has been found to be very destructive to the fry of the Black-spotted Trout in Colorado, U.S. Fish. Rep. Bull. 1902, p. 158.
For figures of Protohydra see Chun, Bronn's Thier-Reich, "Coelenterata," 1894, Bd. ii. pl. ii.
Sitzber. Ges. naturf. Freunde Berlin, ix. 1894, p. 226.