83 271 



Rattulus stylatus (Gosse). 

 Tab. III, flg. 5. 



Description. Body pearshaped, rather soft willi thin hyaline culicida, pre- 

 senting three rather well-marked transversal lines; wheel-organ a terminally situated 

 disc, surrounded by a wreath of rather short cilia; the disc itself covered with short 

 hairs, in the middle a tuft of long, strongly developed iiairs. No antennæ ol)serve(l. 

 A brain with a large red irregular eye-spot. The whole body cavity filled with a 

 grejàsh mass, containing numerous oil-globules. In this mass a very large almost 

 globular testis, reaching up before the eye; two sorts of spermatozoa; the testis opens 

 into a peculiar chitinized penis-tube which ends in a disc with the opening of the 

 penis in the middle of the disc; the penistube can be withdrawn and again protruded. 

 I have been unable to find any remains of an alimentary canal, of excretory organ, 

 retrocerebral organ, antennæ, prostata or. even muscles in the male; I suppose that 

 the muscles, at all events, may have been present. Size of male 60 //, of female 

 140— 180/(, 



In one of my experimental ponds near Hillerød R. shjiatns is very common; 

 it has a large maximum in May; when I had isolated from the lighted border of 

 the vessel many hundred females, the males appeared. The eggs were laid on the 

 bottom, and the extremely small and extremely rapid males appeared. 



Rattulus pusillus (Lauterborn.) 

 Tab. Ill, fig. 6. 



Description. Body pyriform, hyaline with a rather soft cuticula furnished in 

 front with a peculiar system of longitudinal folds, by means of which the cuticula 

 can be folded over the wheel-organ, when this is drawn in ; at the posterior end an 

 inconspicuous cleft; a wheel-organ which can be placed vertically on the longitudinal 

 axis and be bent slightly ventrallj'. It consists of a wreath of short cilia, surrounding 

 a cilia-covered disc with a protuberance bearing a tuft of cilia. The brain is very 

 large, sending two nerves to a little dorsal antennal organ; a large red eye is situated 

 on the underside. Testis large, globular with two prostata glands; the penis chitinized, 

 somewhat curved, ending again in a somewhat hollowed circular disc with a central 

 opening; two sorts of spermatozoa. No trace of alimentär}' canal, excretory organ, or 

 retrocerebral organ; lateral antennæ have been observed; four very conspicuous trans- 

 versal muscle bands, but no longitudinal muscles have been seen. Size of male (50 ,«, 

 of female 115 //. 



R. pusilhis was found common on 3/VIII 1921 in a pond near Sorø; of other 

 Rotifers there were only Aniircva hijpelasma and Sijnchcvla oblonga in the sample. 

 Having taken a proof with many hundreds of R. piisiUiis in a little cup, the next day 

 I had more than twenty males which were hatched from eggs laid on the bottom 

 during the night. The males were extremely rapid; three times I observed the mating 

 process, the male sitting on the back of the female. Eight days later R. pusillus was 



36* 



