ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 789 



portion or the whole of the protoplasm being used up in the forma- 

 tion of zoospores, which process is a very rapid one. On escaping 

 from the zoosporangium these bodies are minute pear-shaped or 

 ovoid masses of protoplasm, containing granulations, and not invested 

 with a cell-wall, provided at one end with a flagelliform cilium, and 

 also with a contractile vacuole. In some cases the zoospores are 

 unable to escape from their parent cell, and transform themselves 

 directly into new zoosporangia. Either the ordinary zoospores or 

 those derived from these secondary zoosporangia, after moving about 

 actively for half an hour, lose their cilium, and become transformed 

 into an ordinary amoeboid mass of protoplasm, with movements due 

 to contractions and dilations, in which condition they may be 

 described as myxamoehce. In this state they not unfrequently come 

 together and coalesce, the two vacuoles remaining for a time dis- 

 tinct, but finally uniting. The original plasmodia are formed either 

 from a single mysamoeba, or result from a fusion of several ; and these 

 may then propagate themselves for several generations before the 

 formation of zoospores. 



Instead of the production of zoospores, the period of vegetative 

 activity of Protochytrium is frequently closed by the formation of 

 cysts, or true encysted plasmodia, especially at the period when the 

 host naturally dies. These are cells with double walls, and with a 

 considerable space between the outer and inner walls ; this space is 

 filled with a transparent fluid, often containing small remains of 

 nutrient substance not completely digested. The ordinary diameter 

 of the cyst itself is from 15 to 25 /x, that of the external envelope 

 from 30 to 40 /a. This external envelope displays many of the pro- 

 perties of fungus cellulose. The internal contents consist of a dense 

 finely granular protoplasm. These cysts are formed within the cells 

 of the host, and when they decay, fall to the bottom of the water, 

 where they germinate after a period of rest, and develope into 

 myxamcebae. These again enter the cells of the host by penetrating 

 through the cell-walls, in the same manner as the germs of many 

 Chytridiaceae. 



As regards its systematic position, Protochytrium displays on the 

 one hand affinities with the Myxomycetes, and on the other hand 

 with such genera of ChytridiaceaB as Woronina, Bozella, and Olpidi- 

 ojjsis ; but the author considers the entire absence of a cell-nucleus 

 to be a point of so great morphological importance that it must for 

 the present be referred to Klein's family of Hydromyxacese, along 

 with the forms of Manas described by Cienkowski and Hackelj and 

 also Vampyrella, Monadopsis, and Protomyxa. 



Licheues. 



Substratum of Lichens.* — 0. J. Richard, besides combatting the 

 theory of an algo-lichonic association, holds that the nature of the 

 substratum, whether calcareous, siliceous, metallic, organic, or neutral, 



♦ Actea Soc-. Linn. liordciiux, 88 pp. Sec Bull. Soc. Bot. France, xxx. (1883) 

 Kev. Dibl., [ip. 105-7. 



