320 132 



water, the question arises from where this enormous water current comes. Further, 

 where are tlie forces which uninterruptedly drive the currents through tlie body 

 cavity and wliere are tlie openings, through which the water finds its way into it? 

 And lastly why should the body cavity be run through by such enormous water- 

 masses? CoHN, CosMOvici and Jansen have supposed that the bladder is in some 

 way filled from the alimentary canal, and that its main task is to can-y out of the 

 body the water-masses which the animal has taken in through the mouth together 

 with the food. "Sie hat, entgegen den früheren Ansichten, die Aufgabe, den durch die 

 Räderorgane mit den Nahrungsteilchen in den Verdauungskanal hineingetrudelten 

 Wasserslrom, der durch die starke Bewimperung des letzteren weiterbefördert wird, 

 zu sammeln. Die Blase d. h. der dehnbare, dünnwandige Teil des Enddarmes wird 

 durch das gesammelte Wasser aufgebläht und befordert dasselbe periodenweise durch 

 Zusammenziehung nach aussen" (Janson 1898, p. 8). Janson further shows that the 

 vesicle was contracted everj' 18 seconds, if the wheel-organ was fully expanded. If 

 it was contracted, the contractions of the bladder were slower, first every twenty 

 seconds, then every 25, 30, 40, 50 seconds and lastly they almost totally dis- 

 appeared. As soon as the wheel-organ was again expanded, the contractions — about 

 four in a minute — began again. According to Janson this can only be interpreted 

 to mean that the water is forced into the alimentary canal through the mouth, passes 

 through the alimentary canal into the bladder, from which it is again poured out. 

 Owing to the peculiar derivation and position of the contractile vesicle in the Bdel- 

 loida, the explanation of Cosmovici and Janson may be correct for these animals; 

 but in the other divisions of the Rotifera it is difficult to understand that it can be 

 quite exhaustive. The same ideas have, by the way, been set forth hy Willem (1910, 

 p. 26), who supposes that the watermasses especially pass through the thin walls 

 of the oesophagus, and by Gosse (1889, p. 138), who maintains that they "pass at 

 the head." 



In the male sex the excretory organ is only fully developed in the genus 

 Asplanchna. Exactly as in the females we here find the two sorts of lateral canals, 

 the secreting glandular tubes and the excreting capillary tubes which carry the vi- 

 bratile tags. In the different species we find the same great difference with regard 

 to the number of tags in the male sex as in the female sex; in A. priodonta in both 

 sexes from 4 to 5 in A. Sieboldi about 40 — 50. The two lateral canals as in the 

 female open in the contractile vesicle, and this again opens into the ductus semi- 

 nalis. The vesicle is filled and contracted as far as I have been able to see quite 

 in the same manner in the male as in the female. Fully extended it reaches an 

 enormous size, in the male of A. Sieboldi, more than ^/s of the body cavity. Apart 

 from the Asplanchnas the contractile vesicle seems to be absent in almost all other 

 Rotifer males. The two lateral canals which show a more simplified structure in 

 the males than in the females, almost always seem to open with two small openings 

 at the sides of the opening for the penis; but these openings are difficult to see. 

 I for my own part have only been able to see them with certainty in Salpina, 



