272 84 



only found in very small numbers. Males which were isolated one day in the mor- 

 ning, were always dead before evening; most probablj^ they only live some few hours. 



Rattulus cylindricus (Imhof). 

 Tab. Ill, fig. 8. 



Description. Body somewhat edged, much broader in front than behind, a 

 soft hyaline cuticula with lines which seem to indicate a rather incomplete lorica ; a 

 deep transversal furrow divides the body into a forepart, faintly longitudinally folded 

 in such a way that this part can be folded round the retracted wheel-organ; a 

 posterior part attenuating posteriorly ; dorsally this part, when faintly compressed, 

 shows lines which are indicated on the figure. The wheel-organ shows a circle of 

 rather short cilia and on the disc, three tufts of hairs; of these the median is most 

 strongly developed: above it, a very conspicuous fleshy antenna; a broad brain; no 

 eye spot; dorsally a well-developed dorsal antenna and sidewards two conspicuous 

 lateral antennæ, each with a strongly developed sensitive hair. Of the excretory organ 

 two short canals, each bearing two vibratile tags, are seen; no contractile vesicle. 

 A very large globular testis, containing the two sorts of spermatozoa, and above it 

 a very large oilglobule, surrounded by an irregular, often quadrangular dark mass. 

 On the sides of the testis two large prostata glands. The testis debouches into a 

 strongly developed, protrusile penis-tube, chitinised, but, as far as I could see, pro- 

 vided inside with cilia and ending in a disc with the penis opening lying centrally. 

 No trace of alimentary canal. The whole body containing numerous oilglobules. Size 

 of male 80 /*, of female 300 //-. 



R. cylindricus is rather common in many of our smaller lakes; in contrast to 

 almost all the other members of its genus it is a real plancton organism; as such 

 it carries its eggs; of the female eggs only one or two; of the male eggs a small 

 chain of three or four eggs ; of these females carrying male eggs I have isolated several, 

 hatched the males and seen them in great numbers in my vessels; they were ex- 

 tremely rapid and very difficult to isolate and study. Their form was more flattened 

 than in the other species described; the large oilglobule and the numerous other 

 globules, deposited round the organs, may be regarded as plancton characters. 



General remarks. 

 As the males of Diurella have hitherto been entirely unknown, we are unable 

 to indicate the family character of the males. With regard to Rattulus it may be 

 pointed out that the males are extremely small, onl}' measuring about V^ to Vi of 

 the female. They lack every trace of a foot, the long differentlj' formed toes, and the 

 foot glands so highly developed especially in this family; also, all indications of a 

 carina and thorns on the forepart of the lorica are absent. The body is only a cy- 

 lindrical or flattened sack with a faintly developed lorica. The wheel-organ is a 

 terminally situated disc, surrounded by a wreath of cilia, and on the disc some 

 bunches of long bristles; when retracted, the forepart of the body is folded over it. 



