282 Mr. IK, J. Carter on the Organization of Infusoria. 



were rarely ejected portions of the "abdominal mucus" of 

 OtosUma, which, assuming a spherical form, and containing 

 id pellets of half-digested vegetable matter, which had in 

 consequence become of a bright brown colour, so simulated the 

 bile-cells of Planaria, that, at the time, I set them down as 

 identical. No such cells occur in the Infusoria that I have since 

 been able to see ; and therefore " spherical cells," in my list of 

 the organs of the Infusoria, should be erased. 



Vesicula. 



At page 126 ibidem, I have described the " contracting vesicle" 

 under the name of " vesicula," as being a more appropriate and 

 more convenient term, and have assigned to it an excretory 

 function ; but this has been disputed, and therefore I would 

 now add more to strengthen my inference. 



In their ' Etudes sur les Infusoires, &c.' (p. 42 et seq.), MM. 

 Claparede and Lachmann have come to the conclusion that the 

 vesicula is not an excretory organ ; and in Pritchard's ' Infusoria ' 

 (4th ed. p. 432, 1861) it is stated that Colin, in Brachionus mili- 

 taris (which has a sinus attached to the vesicula), has "decisively 

 proved, by mingling colouring matter in the water and witness- 

 ing a current inwards during each dilatation, and one outwards 

 on each contraction, alternately, that it not only opens into the 

 cloaca, but that it is a respiratory organ." 



As regards MM. Claparede and Lachmann's conclusion, I 

 would observe that, throughout their excellent article on the 

 subject, while they endeavour to maintain that the fluid of the 

 vesicula is returned into the vessels on the systole or contraction 

 of the vesicula because the sinuses and vessels become filled 

 immediately afterwards, they never once allude to the possibility 

 that this may take place from the closing of the valves between 

 the sinuses and vesicula at the moment the latter is about to 

 eject its contents externally, which, after careful re-examination, 

 would be my explanation of the phenomenon : viz. the fluid, still 

 flowing on towards the vesicula, like that of the blood towards 

 the heart, is ponded back for the moment in the sinuses and 

 vessels, while the vesicula empties itself, like the ventricles of 

 the heart, in another direction. 



If we watch the vesicula in Paramecium aurelia as this animal 

 gradually rotates itself upon its long axis, we observe that it 

 is situated peripherally; that when distended and uppermost 

 (nearest the observer) it is spherical in appearance, and presents 

 a small papilla in the centre; and that when it is lateral it 

 is bottle-shaped, the neck communicating with the papilla. 

 Further, we observe that the sinuses are attached round the 

 shoulders of the bottle, and that when the diastole or dilatation 



