OF THE ROTATORIA. 429 



without into the general cavity of the body, its percolation through ^* short 

 lateral vessels " (the oscillatory^ tags) into the winding canal of the lateral 

 band of each side, and its passage thence into the contractile vesicle, by which 

 it is pumped out through the cloaca. This process Siebold designated a water- 

 circulating system. 



Mr. Dakymple, in his excellent description of a supposed new Notommata 

 (the Asplanclma Brightwellii of Gosse), differs from Siebold in the account 

 of the respiratory apparatus in several particulars. He says — '' This pecu- 

 liar organ consists in a double series of transparent filaments (for there is no 

 proof of their being tubes or vessels), arranged, from above downwards, in 

 curved or semicircular form, symmetrical when viewed in front (XXXVI. 

 6 a a). These filaments, above and below, are interlaced, loop -like, while 

 another fine filament passes in a straight line like the chord of an arc, uniting 

 the two looped extremities. To this delicate filament are attached little tags 

 or appendices, whose free extremities are directed towards the interior of the 

 animal, and are effected by a tremulous, apparently spiral motion, like the 

 threads of a screw. This is undoubtedly due to cilia arranged round these 

 minute appendices. The tags are from eight to twelve, or even twenty, in 

 number, varying in different specimens (XXXVI. 6). 



" I beheve the organ in question to be a peculiar circulatory system. The 

 body of the animal is filled with fluid, most probably analogous to blood, 

 while the ciliated tags, in perpetual motion, must produce currents in this 

 fluid, and probably iu a uniform and determinate dii^ection. In this way the 

 nutrient plasma will be brought regularly ia contact with all parts of the 

 body, and the process of nutrition go on as in insects, mthout the interven- 

 tion of tubular vessels, — the dorsal heart in them serving only to give direc- 

 tion and circulation to the blood. I am the more impressed with this belief, 

 since these filamentous organs are in close approximation with the large con- 

 tractile sac, which probably performs a respiratory function." 



Moreover Mr. Daliymple does not believe in any communication between 

 the sac and the apparatus furnished with the ciliated tags, as Siebold supposes ; 

 on the contrary, he represents the sac to commimicate directly with the ex- 

 terior. He writes — " This sac, spherical when distended, is placed just 

 above the ovisac, and communicates with the vaginal canal. It is ex- 

 ceedingly delicate, and may be seen to contract, by the action of muscular 

 fibres, with great rapidity, in which act it is thrown into numerous regular 

 folds or pouches, and in that condition appears not very dissimilar to the 

 large cellular limgs of Batrachia .... The explanation which I venture to give 

 is, that this sac draws in water and expels it again by the vaginal orifice ; 

 and it is by bringing the blood, by means of the ciliary movements of the 

 tags, into immediate contact (the delicate membranous wall of the sac in- 

 tervening) with the air of the water, that aeration or respii-ation is per- 

 formed. An analogous contractile sac may be seen in Rotifer vulgaris.'' 



Lastly, the author adds that he is convinced, from repeated observation, 

 that the contractile sac has no relation with the generative function, and 

 that *' the supposed vascular ramifications upon it are neither more nor less 

 than the muscular fibrillae by which the contractions are effected." 



Perty coincides with the explanation offered by Daliymple, and reproduces 

 it in his work. Mr. Gosse presents, in his notice of AsjyJanchna 2>^odonta, 

 the following description of the mechanism in question : — " On the upper 

 side of the oviduct sits a contractile bladder, which, when full, is perfectly 

 globular and small, being scarcely, if at all, larger than the two pancreatic 

 glands put together. Eound this, attached at or near its base, passes on each 

 side a tortuous thread, apparently glandular, which goes up along each side 



