416 J-:. .1. AIJ.MN AND K. \V. NELSON. 



Besides diatoms, many otlier ort^anisms appear in these 

 cultures. We are indebted to Mv. G. S. West for the 

 identification of a foini of unicelhilar al<(a, which is very 

 common and difficult to avoid when attempting to o})tain 

 persistent cultures of the Diatomaceae, namely, Pleuro- 

 coccus mucosus (Kutz.) Rabenh. This small green alga, if 

 once introduced into a culture of a plankton diatom, will soon 

 multiply at the expense of the latter with its ultimate extinc- 

 tion. It is very hardy, and cultures of it in almost every 

 medium seem to last indefinitely. Multiplication Ijeyoiid a 

 certain point probably does not occur, but the cells letain 

 their colour and normal shape, and will start active repro- 

 duction if suitable nutrient material is provided. 



In cultures inoculated from ])lankton, many other forms of 

 unicellular and filamentous algte thrive. Several species 

 belonging to the classes Ehodophy ceae and Myxophj-cete 

 commonly occur, but we have not been able to identify them. 

 The most usual filamentous forms of C h lorophycete are 

 Enteromorpha, A'auchera, Khizocloni u m, etc. It is 

 interesting to note that it was the unintentional appearance 

 of young plants of Laminaria digitata in some of our 

 Petri dishes that led Mr. Drew (4) to cultivate this alga in 

 Miquel sea-water and so discover its early life- history. 

 Cultivations of marine algas by these methods would without 

 doubt yield many new species, and would also provide rich 

 material for the study of their modes of reproduction. 



Many forms of flagellates live either together with diatoms 

 or alone. Among. these is an unidentified species of Chilo- 

 monas, which we have obtained in persistent culture. It 

 multiplies very rapidly, colouring the whole medium a deep 

 red-browai. It flourishes in Miquel sea-water and its nutrition 

 is evidently autotrophic. In one culture, in Miquel sea-water 

 inoculated with plankton, a number of coccospheres developed, 

 probably Coccosphfera atlantica Ostenf. Other flagellates 

 and ciliated infusoria are very commonly met with, such as 

 Bodo, Euplotes, Euglena, etc., which all seem to depend 

 on the diatoms or other vegetable organisms for their food 

 material. 



