Distribution of Pelmatohydra oligactis (Pallas) in Scotland

Abstract

SINCE 1918, Hydra vulgaris attenuata and Hydra vulgaris vulgaris have been cultivated in the Notre Dame Laboratory for teaching purposes. Very occasionally these cultures have had to be replenished from outside sources. It was not until 1946 that I noticed the occurrence of Pelmatohydra oligactis, which I felt sure had been introduced in material obtained from a dealer in the south of England. The Hydra vulgaris vulgaris were completely ousted by the rapid spread of Pelmatohydra oligactis. In October 1947 all the specimens were reproducing luxuriantly; even small individuals were covered with testes. After this efflorescence, the organisms gave place to Hydra vulgaris vulgaris.