64 TERATOLOGY OF DIATOMS. 



But not only the exterior of the diatom frustule suffers from the attacks 

 of parasites ; Dr. W. Zopf has described under the name of Ectrogdla 

 Bacillariacearum, a fungus which lives in the interior of living diatoms 

 and specially attacks Synedra and Pinnularia. 



Its presence is manifested in the first place by an alteration in the shape 

 and position of the chromatophores. The latter recede from the walls, 

 contract in the direction of their length, and conclude by being closely 

 applied to the parasites. At the same time the nucleus is dissolved, and the 

 protoplasm contracts. Later on, in consequence of the growth of the 

 parasite, and of the pressure which it exercises on the valves, the latter 

 open, and the parasite can emit its spores exteriorly. 



At a meeting in London of the Royal Microscopical Society on the 19th 

 October, 1892, Mr. C. Haughton Gill exhibited frustules of Pleurosigma, 

 Nitzschia, and Cymbella, infested with a fungus. Mr. Gill was good 

 enough to forward me photographs of the parasite and of his preparations, 

 showing the latter in various stages of growth. In the letter, which accom- 

 panies the packet, our kind and learned correspondent expresses himself 

 thus : " The fungus, if not directly identical with, appears to bear a consider- 

 able resemblance to Zopfs Edrogella bacillariacearum (Nov. act. der Kol. and 

 Leop-Carol Deutschet Akad. xlvii. p. 145). In some respects it resembles 

 even more closely the Olpidiopsis described by Cornu (Ann. des Sc. Nat. 

 series 5, xv.) as infesting Saprolegnia;. The sporangia, which first make 

 their appearance (in Pleurosigma attenuatum) at about the beginning of 

 November, are at first of a plain sausage-shaped outline, and their contents 

 are nearly homogeneous. As they arrive at maturity, granules appear in the 

 interior, and shortly afterwards the thick wall of cellulose becomes tumid at 

 one point, and a beak or tube of ejection is put forth you will find more 

 than one spore sac at this very stage (on the slide tinged with black) detached 

 from the shell of the diatom. 



"After some time the beak or tube bursts at its extremity and the zoospores 

 issue rapidly into the surrounding water. I have not yet traced the 

 further history of these zoospores. 



"A very curious point, which greatly needs confirmation by other observers, 

 is this this parasite appears in Pleurosigma attenuatum in November, 

 December, and January. I have been hitherto quite unable to find it 

 either before or after those months in this particular diatom, and during 

 those months I have found it in no other species, though Nitzschia, 

 Cocconemct, Pinnularia, etc., were abundant and were kept observed under 

 identical conditions (in the same dish of water). About March the Nitzschia 

 and Bacillaria became infested, while the Pleurosigma remained healthy 



