13 201 



to conjecture that llic species in this locality only propagates ijaiihenogenclically. 

 For many years this investigation lolalh' lacked the males of very many genera, 

 even such in which the males were descrihed by earlier authors. Maxima were ob- 

 served, sexual periods, however, not. 



In 1920 — 22 a rather extensive investigation relating to Ihe study of the sexual 

 propagation in Oligochœta was planned. It was shown that the Oligochœta, in those 

 periods when the sexual products were to ripen, were in search of those algæ-carpefs 

 which cover the surface of small ponds like scum, especiallj' at the highest summer 

 temperatures. It was further shown that the tp. in these algæ carpets might in spring 

 rise to about twenty-eight degrees celsius, even if the tp. a few inches below the 

 surface was only about 18 — 20 C. Undoubtedly the worms used the extremely high 

 temperatures to ripen the sexual products; very many of our Oligochæta hitherto 

 regarded as rare f. i. Vejdoiuskijella, Pristina, Slavina, Kipistes were found here, and 

 almost all were found in the sexual period, this being for many of the species either 

 totally unknown, or at all events only observed rarely. The investigation, carried on 

 by one of my assistants Mag. Lakjer, whose death was a great loss to my labo- 

 ratorj', induced a wish on my part to see whether the Rotifera did not also use 

 the algæ carpets in the same way as the Oligochæta. My idea was correct, and it 

 was shown that in the very same ponds, in which I had for years been in search 

 of Rotifer males, belonging to species which were extremely common here in the 

 female sex, and of which, nevertheless, I never saw any of the males, the latter 

 could be procured as soon as the algæ carpets were peeled off from the surface by 

 means of glassplates. These algæ carpets acted as a substratum upon the underside 

 of which very many creeping Rotifers, at other times of the year living in the littoral 

 or upon the bottom of the pond, were to be found in great numbers in the sexual 

 period. Almost all the Rotifera which passed their sexual periods on the undersurface 

 of the algæ carpets, belonged to the creeping or slowly swimming species. Just these 

 species hardly ever carry their eggs; they were deposited upon the underside of the 

 carpets and owing to the high temperatures ripened there in the course of very 

 few hours. 



On the algæ carpets in various pitholes, on the same moor, different Rotifers would 

 simultaneously show great maxima; in seven pitholes on the same moor I simul- 

 taneously found maxima of Salpina miicronata, Metopidia triplera, Eiichlanis dilafata, 

 Triphijlus laciistris, Copeiis lahiatiis, Dinocharia pocilliim, Scaridiiim longicaiidiim. 



Commonly every little pithole had almost pure cultures of the dilTerent species; 

 a more thorough investigation further showed that the different species succeeded 

 each other in the hole; in one pithole great maxima of Eiicljlanis dilatata, Dinocharis 

 pocillum, Scariditiin loiigicaiidum and Tripbijhia lacastris succeeded each other serially. 

 The algæ carpets came on the surface in the middle of May at an airlp. of about 

 18 — 20° C, they were used by the Oligochæta and Rotifera (most probably also by 

 some Copepoda, especially Harpacticidw, and Ostracoda), till the lirst part of July; 

 then very high summer temperatures set in, and the tp. in the algæ carpets reached 



