OF THE PROTOZOA. CILIATA. 323 



pear-shaped reservoirs, vdth points directed outwards in the shape of a 

 star. In the pulsation of these strange star-shaped reservoii's sometimes 

 the stars disappear entirely, sometimes only the central roimd spaces, and 

 sometimes only the rays.' The opaque Bursarice exhibit this phenomenon 

 just in the same way as it is described by Yon Siebold ; and those speci- 

 mens in which the vascular system can be detected, offer the explanation 

 of it. The small pear-shaped spaces are really the commencciments of the 

 vessels, which expand with the accumulated fluid ; and the rays are the 

 further prolongations of the same, which may be traced to the ends of the 

 body. 



" At the moment when the contractile vesicle has attained the greatest ex- 

 pansion (that is, when the diastole is terminated), it appears in the form of a 

 globe filled T\ith colourless fluid, from which the vessels run out on all sides 

 in the cortical substance as canals, apparently of equal diameter ; they have 

 at this time the smallest diameter they can assume at their embouchure into 

 the reservoir. In opaque specimens, this is the moment when the opened 

 contractile vesicle is observed. A little before we observe the commencement 

 of the systole, the vessels begin to expand slowly, at points distant about one 

 diameter of the contractile vesicle from the surface of the latter, to many times 

 their original size. The more the systole progresses, the wider and longer 

 become the swoUen places, and they approach gradually to the contractile 

 vesicle. If we make an observation at the moment when the diameter of the 

 contractile vesicle is diminished to about one-fom^th of its original size, the 

 shape of the apparatus agrees in all essential points with the weU-known 

 stellate figure represented by Dujardin in Paramecium Aurella, with the 

 single exception that the embouchui^es of the rays are distinctly visible, and 

 theu' peripheral prolongations run out widely in the form of canals over the 

 entire animalcule. Opaque specimens of the Bursaria display the phenome- 

 non only in such a degree that the rays terminate in delicate attenuated 

 points, at a distance of about one diameter of the reservoir from the latter. 

 When the contractile vesicle has closed completely, the fusiformly- expanded 

 vessels only are seen, as they run together with theu' apices to one point. 

 This completes the systole. The diastole then recommences. If we examine 

 the animal at the moment when the reservoir has again attained half its 

 greatest diameter, we find a totally different appearance fi^om that at the cor- 

 responding epoch of the systole. The vessels are not expanded now in the 

 form of a spindle, but of a funnel, with the base of the funnel in the contrac- 

 tile vesicle, and the point prolonged out into the vessel. This is the form 

 which Ehrenberg has figured in Paramecium Aurella, only omitting the fur- 

 ther prolongations of the vessels. Yon Siebold rejects Ehrenberg's figure 

 and recognizes Dujardin's; but both are really correct, only representing 

 different instants ; Dujardin gives a stage of the systole, Ehi'enberg of the 

 diastole. 



" The more the contractile vesicle now expands, the more is the depth of 

 the funnel decreased, and its diameter proportionately increased ; or, in other 

 words, the vessel expands only at its embouchure, and the depth of the ex- 

 panded part decreases in proportion with the advance of the diastole. In 

 opaque Bursarice we see at this time only the contractile vesicle produced out 

 in various directions into short funnel-shaped processes. By degrees these 

 processes entii^ely disappear, — the contractile vesicle having expanded to its 

 original volume. We now see again how, from the fully-expanded contrac- 

 tile vesicle, the whole of the vessels run out in the cortical layer, in aU di- 

 rections, as slender streaks ; in opaque specimens only the contractile reser- 

 voii' is visible. 



y2 



