318 130 



lateral organs, which are difficult to observe, and probably often overlooked. In the 

 sessile families the Flosculariidœ and Melicertidœ, where the sense organs in the 

 female sex show so many peculiar structures, they seem to be very much simplified 

 in the male sex, and are never elongated into long antenna-like organs. 



Most of the Rotifers possess sense organs for light in the female sex. They 

 are lacking in Pleurotrocha, Xoteus, Callidina, Adineta-s]pecies, and in the Flosculariidœ 

 and Melicertidœ, when sessile; in the freeswimming stage they possess two eye spots. 

 In accordance with de Beal'Ch.a.mp the position of the eye spots in Rotifera may be 

 referred to the following scheme: an eye occipitale, often double and in contact 

 with the brain, and the retrocerebral organ and two superior eyes on the disc or 

 in the corona. As far as I know, the two sorts of light percei"ving organs do not as 

 a rule occur simultaneously. The common occurrence is the unpaired eye spot, below 

 the brain; we have here a simple pigmented spot, a typical lens has not often been 

 observed ; it is however possible that the bacteroides in some species f. i. A', pseudo- 

 cerberiis, being situated in contact with the eye spot, and on its underside, may play 

 a secondary rôle as light perceiving (de Beauchamp 1909, p. 174). Two eye spots 

 exist in Pterodinidœ, Pedalionidæ, Coluridœ, in some of the Xotommatidœ (Diglena) 

 and a few Asplanchna-species. In the genus Rotifer they are placed upon the tip of 

 the proboscis; as mentioned above they occur in the freeswimming stage of Flos- 

 culariidœ and Melicertidœ- but very often disappear in the fixed stage. Two eye spots 

 lateral also occur in Eosphora-species, but according to Hirschfelder (1910, p. 86) 

 these spots are not eye spots. 



In the male sex it is interesting to see, that the number and position of the 

 eye spots are almost always in accordance with those of the female. In those females 

 which have one single eye spot, this is also found in the males; and when the fe- 

 males have two anterior eye spots, this is also the case with the males; in the Eos- 

 phora males we find three "eyes" as in the female; also the position of the eyes 

 in the males of Asplanchna, is the same as in the females. This is also the case 

 with Triarthra, but here as well as in the Flosculariidœ it must be emphazised that 

 the two eye spots in the male sex are placed upon a hill-like prolongation which, 

 especially in Triarthra, has almost the character of a proboscis. In Rhinops the eye 

 spots are situated upon the proboscis-like prolongation in both sexes. Especially in 

 Triarthra and Pedalion typical lens organs have been observed. In some of the 

 most reduced males I have been unable to find any trace of eye spots {Polyarthra, 

 Gastropus, Ploesomd). 



Xephridia. As well known, the nephridia of the Rotifera consist of two 

 lateral canals, equipped with a number of vibratile tags and opening into the con- 

 tractile bladder, which again debouches in the rectum. Commonly a transversal com- 

 missure between the two longitudinal canals is not observed; hitherto it has only 

 been detected in Stephanoceros, Atrochiis, Conochiloides natans, Apsilus, Lascinularia and 

 Hydatina; it must however be remembered that just these Rotifers are the best 

 studied of all. Everywhere where more elaborate investigations are carried on, it 



