172 Transactions of the Society. 



Resting-egg of Synchseta pectinata. 



In my description of this species in 1902 I mentioned that no 

 fertilised resting-egg, indicating the presence of a male, had yet 

 been seen by any observer. 



This has since been found in 1903 by Dr. St. Hlava, of Prag, 

 who was good enough to send me a female containing an undoubted 

 resting-egg, and in June last year I found a similar egg within the 

 body cavity of a female. It is spherical in shape, the surface 

 covered with short rounded projections as figured in plate V. 

 fig. 3, and yellowish-brown in colour. 



The size is 100 fi (^q in.) in diameter. 



Though the female is very abundant at all seasons, and has 

 been observed for years by many, the male has so far still eluded 

 detection. 



Dr. Wesenberg-Lund has in his recent great Plankton work * 

 expressed the opinion that Synchseta pectinata, tremula, oblonga, 

 stylata, and grandis are only seasonal variations of one species. 

 I think I ought to take this opportunity to express my dissent 

 from this view, as being quite opposed to my experience of these 

 species. 



S. pectinata, tremula, and oblonga are common forms, which 

 appear, disappear, and reappear all the year round (just like 

 Polyarthra, Triarthra, and other Eotifers), and are not uncom- 

 monly all present together at the same time. In the Grand 

 Junction Canal, running on the north side of London, where 

 I frequently collect, these three species were all present in great 

 abundance, with some half-a-dozen other species of Eotifers, at 

 the end of December, and S. pectinata and oblonga still persist at 

 the present time (March), whilst S. tremula has temporarily dis- 

 appeared. 



S. pectinata is very rarely absent from this canal, and it is 

 certainly there in spring, summer, autumn, and winter, without 

 any appreciable difference in size. Further, these various species 

 have distinctive organs, their lateral antennas are in different posi- 

 tions, and, above all, they have different types of jaws. Thus it 

 is not merely a question of size or elongation of the body ; whilst 

 the seasonal variation, which has been demonstrated in the case of 

 Asplanchna priodonta, consists of a lengthening of the body only 

 during the summer months. A further consideration is, that of all 

 Plankton Eotifers the Synchseta are the most vigorous swimmers, 

 and quite able to counteract by their cilia any slight tendency to 

 sink that may be due to a decrease in the density and viscosity of 

 the water in summer. 



* Plankton Investigations of the Danish Lakes, Copenhagen, 1908. 



