326 SYDNEY J. HTOKSON. 



dniMng conjugation and gemmation might yield results of 

 interest and importance. 



I have had preparations of Deudroco metes under observa- 

 tion for a considerable number of years^ but it was not until 

 1899 that I obtained specimens which clearly showed the 

 mitotic figures of the division of the micronuclei^ and then I 

 determined to investigate the matter with greater thorough- 

 ness. I may explain that during the last two years I have 

 entrusted the mounting of tlie preparations, as well as the 

 staining and cutting of the sections, to Mr. J. T. Wadsworth, 

 and that he has saved me an immense amount of time and 

 labour in pointing out to me the slides that exhibited interest- 

 ing features, and in keeping a catalogue of the preparations. 

 The discoveries therefore that are here recorded were, in the 

 first instance, made by him, and I have to acknowledge here 

 his unfailing assistance and perseverance in the investigation. 



The structure of Dendrocometes has been investigated by 

 Biitschli (1), Wrzesniewski (27), Plate (21), Maupas (19), 

 Schneider (24), and Sand (23) ; but, notwithstanding their 

 excellent work, many points of interest and importance re- 

 main to be illustrated and described. 



Dendrocometes paradoxus is found attached to the 

 gills of Gammarus at all times of the year, but in the summer 

 months there are usually fewer specimens on each gill than 

 in the spring and autumn. We have found that by keeping 

 about twelve or fourteen Gammarus in a shallow pie-dish 

 containing an inch or two of water, with a little mud and 

 waterweed at the bottom of it, the number of Dendrocometes 

 on the gills increases, and that in a fortnight's time a con- 

 siderable number of pairs may usually be found in a state of 

 conjugation. 



Dendrocometes appears to have a wide geographical dis- 

 tribution. I have found it myself on Gammarus at Oxford, 

 Cambridge, in the neighbourhood of Manchester, and on 

 specimens of Gammarus sent to me by Mr. Bolton from Bir- 

 mingham. It was observed by Prof. Lankester on Gam- 

 marus in the ponds at Hampstead. On the continent of 



