131 319 



has further been shown that the longitudinal canals really consist of two tubes, 

 the secretory one (the ürüsengang Mautini's) with relatively thick walls, ol'ten of 

 glandular structure, and the excretory one (the "Flimmergang" Mahtlm's) or capil- 

 lary tube, which has very thin walls; it is this tube which carries the vibralile 

 tags; the tube with the glandular structure commonly forms one or two windings or 

 meanders in many loops and curves. It has much thicker walls and often contains 

 oil globules. It is of great interest that Hlava has found vibratile "Treibwimpern" 

 (Lacinularia, Megalotrocha) in these tubes. The capillary tube debouches into the 

 maintube by means of one or two transversal commissures. The structure of these 

 two tubes, the excretory and secretory ones, their course and the manner in which 

 they are connected with each other are subject to great variation in the different 

 genera and species. The vibratile tags are connected with the tubes by means of 

 short stalks, and project into the body cavity; their number is commonly from live 

 to. six on each side, but may in some Asplanchna species rise to about fifty. Most 

 of the authors, especially those of recent years, are of opinion that the free broad 

 end is closed; they are here provided with a protoplasmatic plug, which on the part 

 turning towards the body cavity is as a rule provided with two tlagellæ and upon 

 the other part carries the vibratile flames, deriving from many cilia coalescent with 

 each other: they are situated in the open space of the vibratile tags and are in con- 

 stant motion. The canals debouch into the contractile vesicle, the walls of which 

 are extremely thin and provided with very fine muscle threads; often, f. i. in 

 Asplanchna, two large star-like cells with very long threads are observed; these 

 cells have the function of contracting the bladder. This latter is commonly re- 

 garded as originating from the coalescense of the two excretorj' tubes. Only rarely 

 is the vesicle absent (Lacinularia, Tubiculavia}. Here the two lateral canals coalesce 

 into a common unpaired part; this part is in accordance with the contractile vesicle 

 of Rotifers, but regular contractions have not been observed, the last part of the 

 rectum functioning in this way (Hlava). In the Philodinidœ part of the rectum is 

 transformed and used as a contractile vesicle, being capable of rhythmical movements. 

 Commonly the whole organ is only regarded as an excretory organ; through 

 the vibratile tags useless or destructive materia are carried out of the body. Gosse 

 however has supposed that the organ is respiratory, and as well known, Ehrenberg 

 regarded it as the male sexual organ. In most of the Rotifers it may be observed 

 that the bladder suddenlj^ contracts regularly about four times a minute, in Asplanchna 

 priodonta according to Willem (1910, p. 26) 4 times a minute, according to Masius 

 (1890, p. 661) ten tiiiies; in Adineta barbata according to Jansen (1893, p. 8) three 

 to four times; then, in the intervals, it slowly fills again. The size of the bladder 

 differs very much; Willem supposed that, in an Asplanchna, when distended, it is 

 almost V5 of the body volume. In other words, during a time of only one to three 

 hours, the organ was supposed to be able to collect and expel a volume of water, 

 equivalent to the whole volume of the body. Apart from the difficulty of understanding 

 that the body cavity should incessantly be run through by this enormous mass of 



42* 



