of the Pali/ gastric Infusoria. 449 



their contractions did not appear to me to be the same as I had 

 been accustomed to see in other forms. Siebold ascribes to Spi- 

 rostomum ambiguum a contractile reservoir in the form of a long 

 pulsating vessel which runs through the longitudinally-extended 

 abdomen. I have never seen this ; perhaps Siebold has mistaken 

 the two to four rows of cilia, which we have mentioned, for it. 

 In Stentor also, in addition to the large round contractile spaces 

 at the anterior extremity of the abdomen, there are several such 

 spaces extending down the abdomen laterally. In my own ex- 

 aminations on the generative relations of the Stentors which I 

 have already detailed, I have examined several hundred speci- 

 mens, but, except the large contractile cavity, have never seen 

 another situated laterally on the abdomen. Probably Siebold 

 has examined the first stage of development (perhaps as fig. 8). 

 The most important physiological property of this vesicle, as 

 already pointed out, is its contractility. We see how, from time 

 to time, it contracts powerfully, frequently spasmodically, again 

 expands and repeats the contraction. In those cases in which 

 the vesicle exhibits stellate extensions, these are expanded at the 

 base so as to resemble a bulb, just as if some fluid contents had 

 been impelled into them, which however has not been shown to 

 be the case. The contractions in some occur regularly, in others 

 irregularly. With a view to this point I observed, with Schmidt, 

 Paramecium Aurelia, Stylonychia pustulata and Bursaria flava. 

 We found that in P. Aurelia, from the commencement of one 

 contraction to that of the following, six to eight, and in Stylony- 

 chia about ten to twelve seconds elapsed, but that in Bursaria 

 the interval between the recurrence of the contractions was so 

 short that it could not be estimated. Let us test by these ob- 

 servations the general correctness of Siebold' s conclusion, " that 

 there are hollow, rhythmically contractile, as it were, pulsating 

 cavities in various forms, numbers and arrangement." 



As regards the occurrence of contractile vesicles in the sepa- 

 rate families, it has been proved in most of them. Even in the 

 first treatise on this subject * attention was drawn to their pre- 

 sence in the greater number of forms, and instances have since 

 been made known, in Ehrenberg's separate treatises, in which 

 they were shown to exist, although formerly they appeared to be 

 wanting. However, they have not been recognised hitherto in 

 the following families (probably on account of the inadequacy of 

 our optical means or other circumstances) : Vibrionea, Arcellina, 

 Bacillarina, Closterina, Colepina and Dinobryina. 



B. The glands. — In addition to the vesicles, we find in almost 

 all Polygastrica, glands of a somewhat more solid structure than 



* Ehrenberg, I. ult. cit. 

 Ann. §■ Mag. N. Hist. Vol. xviii. Suppl. 2 K 



