280 Transactions of the Society. 



centimetres, were of the characteristic chlorophytal colour and had 

 filaments from 1 to 2 cm. in length. Microscopical examination 

 showed this larger and principal growth to be Myxonema tenue 

 (Ag.) Eabenh. with creeping rhizoidal parts imbedded in the slime 

 or attached to the scales or epidermis ; while inmeshed by this, 

 partly epiphytic, and partly held by slime, were several other 

 healthy but chiefly unicellular algte which are named at the end 

 of this paper. 



It may be recorded here that Myxonema tenue, when found 

 in this locality, is usually in stone-paved gutters in which there 

 is a rapid flow of water, or in other fast-flowing streams, either 

 large or small, sometimes epiphytic on submerged twigs of 

 Salix habylonica, or on the stems and leaves of river-side herbs 

 such as Polygonum minus and Triglochin procera, but more often 

 attached to stones or dead twigs. In the fish-pond, where the 

 water was almost stagnant,- this alga grew, poor in quality, on 

 stems and leaves of macrophytes, but in comparative luxuriance on 

 the backs of at least three fishes. I think that some interest, 

 therefore, attaches to the adaptation of this stream-loving Myxonema, 

 which, finding the almost stagnant water of the pond unsuitable, 

 had, by means of its zoogonidia, obtained a footing, either by 

 accident or design, on moving objects, thus obtaining the desired 

 water-friction to which the species had been accustomed. 



The ultimate effect of the algal growth on the fishes, however, 

 was in each case the premature death of the host, which was 

 preceded by a gradual loosening, in places, of the scales, which 

 eventually dropped off, the fishes probably contributing to the 

 displacement by brushing against projections to relieve themselves 

 of the source of initation. 



Parts of the fish, which bore the algai, showed white patches 

 or small spots in the transparent slime, caused by a fungus, and 

 as the mycelial threads were found also associated with the algse, 

 it is possible, or even probable, that a fungus-growth, set up 

 through an unhealthy condition of the fishes' epidermis or slime, 

 paved the way for the growth of the chlorophyte. In places, also, 

 where the scales of the fishes had dropped or been forced off, the 

 alga had gained a foothold, and thus evidently was not dependent 

 on the scales or the crevices between them, but rather on the slime 

 of the epidermis itself, as sometimes, but not always, a considerable 

 amount of force was required to detach it. 



The following is a list of the algse obtained from a small tuft 

 of Myxonema not more than • 5 cm. in area, the branched filaments 

 being 1 • 5 to 2 cm. long. The Pediastra and unicellular species 

 inmeshed among them may have become attached subsequent to 

 the growth of the Myxonema during the efforts of the fish to rub 

 off the latter against algse-covered objects. 



