shape and are all exactly alike; they swim about for a considerable time and then germinate. Sexual reproduction has as yet not been observed. As regards the mode of life of the alga, from the fact that sections separated from the tortoise can be kept alive for a considerable time, during which the cells can grow and produce zoospores, it would seem that the alga derives no nourishment from the tortoise; yet the alga derives very great benefits from its mode of life, for the tortoise, though spending a great part of its time in water, is able to wander about from pool to pool, and thus conveying the alga with it, effects its distribution geographically. Again, during dry seasons, when a pool of water in which a tortoise infected with the alga becomes dried up, the tortoise is able to migrate to another, and generally does so at night, and hides in the shade during the day; in case it cannot find water in this way, the alga is kept alive by not being exposed to the heat of the sun. We must therefore at present regard the alga as an epiphyte, since at present the observations tend to show that no nourishment is derived from the tortoise. At present, since the sexual reproduction of Dermatophyton is unknown, its proper place in the classification of the Algae cannot be assigned; yet it evidently belongs to the Chlorophycea, and most likely to the Ulvacea, in the family Confervoideæ. The alga described in this paper was first given to me by Professor Moseley, who had discovered it upon some tortoises and who desired me to work out its life-history. I was unable anywhere to find a description of it, and referred it to Professor Boret and to my friend Mr. George Murray, of the British Museum, with a similar result. I delayed to publish a description until I had found some mode of reproduction; and with this object in view I obtained a grant from the Worts Travelling Fund, and proceeded to Portugal in the summer of 1886. As soon as possible on my return, I read a paper before the Cambridge Philosophical Society, where I gave to it the name of Epiclemmydia lusitanica *. It was not until December 1886 that I found that Dr. Peter, of Munich, had published a mere description and had named the alga Dermatophyton radicans on September 22nd of the same year. *Proceedings of Camb. Phil. Soc. vol. vi. pt. i. Nov. 8, 1886. + Bot. Centralbl. Band xxviii. 1886, p. 125; SB. Versamml. deutsch. Naturf. u. Aerzte, Sept. 22, 1885. DESCRIPTION OF PLATE VIII. Fig. 1. Portion dorsal surface of carapace of Clemmys caspica, bearing numerous patches of alga (a, a). Fig. 2. Section of tortoise-shell and alga in a direction perpendicular to animal's back; showing mode of penetration of alga (a) into carapace. Fig. 3. Section of tortoise-shell and alga in direction parallel to animal's back; showing at a, b, c sections through wedges penetrating the tortoise-shell. Fig. 4. Sections grown in water for some few days; showing at a and b the lowermost cells growing into filaments. |