1880.] 



MICKOSCOPICAL JOURNAL. 



151 



just rig-lit, but any flat piece of 

 steel, ii not too heavy or clumsy, 

 will do. The cutting- ed«:e should 

 be about one-foui'th of an ineli 

 wide. Punches and all tools used 

 for cutting wax should always be 

 dipped or moistened in starch, pre- 

 pared precisely as for laundry use. 

 This oj)erates much better than 

 water, or indeed anything else. 



Parasites on Diatoms. 



Prof. J. Brun has contributed 

 some interesting notes on "The 

 Diatoms " to Brehissonia. The 

 article in the last number of that 

 periodical begins with an account 

 of their parasites, which may prove 

 of interest to some readers of the 



JOUUNAL. 



" There is no living creature 

 which has not its parasites ! The dia- 

 toms, small as they are, also have 

 theirs. So it is true that among the 

 creatures infinitely small, we still 

 find " /(? comhat de la vie "and " la 

 hitte poup l- existence,^^ diVi(\. if the 

 large in general eat the small, quite as 

 often the small when united kill the 

 large. Among the diatoms the para- 

 sites are always other algce. 



" Five common diatoms, Witzs- 

 chia linearis and sigmoidea^ Syn- 

 edra splendens and Cymbelld ■macu- 

 lata and cymheforme are some- 

 times found covered with a filamen- 

 tous parasite having the aspect of 

 large, transparent hairs, straight, 

 rigid, and of a very pale yellowish- 

 green. Strongly illuminated and 

 considerably magnified ( x 1200), 

 they appear like a series of vesicles 

 united like a string of beads. This 

 is the Leptothrix rigidula, Kg. 

 The living frustule is not restrained 

 in its movements, and when (under 

 the microscope) it encounters an 

 obstacle in the water, one observes 

 the filaments bend at their base, 

 but reassume their form immediate- 



ly that the obstacle is passed. 

 Coiling in water, or the action of 

 nitric acid, removes the filameiit-s 

 which are not, therefore, of a sili- 

 ceous nature. Potassa distends them 

 and alcohol does not turn them 

 green, thus proving the absence of 

 diatomine. 



" It is evidently this parasite that 

 Ehrenberg (PI. 21, Fig. 11, Edit. 

 1838) and. more recently other 

 naturalists, have taken for motile 

 cilia (organs acting as oars). So 

 said Kiitzing (Baccil., p. 26 and 

 Figs. 61, pi. 3 and 11, pi. 7), which 

 seems to indicate that he considered 

 that these appendages formed part 

 of the diatoms. I have a prejDara- 

 tion in water, in which this same 

 Leptothrix adheres at the same time 

 to Syriedra parmda and to the fil- 

 amentous alga ( Zijgnema ) upon 

 which the Synedr-a is itself a para- 

 site ; also another prepai-ation in 

 which it adheres at the same time 

 to Staurosira parasitiGa, and to ' 

 the NitzscJiia linearis^ which it car- 

 ries, thus affording the curious phe- 

 nomena of three parasites super- 

 posed in a space of five or six 

 hundredths of a millimetre." 



The remainder of the article 

 treats of the development and re- 

 production of diatoms in a very in- 

 teresting manner, concluding with 

 some remarks about collecting them. 



In this connection, the question 

 presents itself, on what grounds 

 can diatoms be classed as parasites ? 

 "We may be willing to admit that 

 the Leptothrix grows as a parasite 

 upon the diatoms, but even this 

 must be regarded as doubtful until 

 it can be proved that the alga draws 

 its nourishment, at least in part, 

 from the diatom. It does not ap- 

 pear, however, that the filaments 

 are parasitic any further than that 

 they are attached to the diatoms. 

 This is a subject that deserves in- 

 vestigation. 



