OF THE PEOTOZOA. CILIATA. 319 



for instance, he thinks he has made out the existence of apertm-es opening 

 on the free surface whether of the alimentaiy tube or of the general integu- 

 ment, close to one or other of which he always finds the vesicle ; and, with 

 this view of the structure, he connects the function of an excretory organ 

 with the sac in question. 



To support this ^iew respecting the ofiice of the contractile vesicle, he ad- 

 vances the following observations {op. cit. p. 126) : — " 1st. It is always seen 

 either close to the pellicula or close to the buccal cavity, and always sta- 

 tionary. Thus, in Paramecium Aurelia it is close to the surface, and although 

 it, of coiu'se, passes out of view as the animalcule tiu-ns on its long axis, yet 

 it always reappears, after contraction, in the same place, — while in Vorticella 

 it is attached to the buccal ca^dty, and, being centricaUy situated, seldom 

 passes out of view, except when it disappears under contraction, after which 

 it also reappears in the same place. 



" 2nd. In Actinophrys Sol and other Amoeha^, during the act of dilatation, 

 the vesicula projects far above the level of the pellicula, even so much so as 

 occasionally to form an elongated, transparent, mammilliform eminence, 

 which, at the moment of contraction, subsides precisely like a blister of some 

 soft tenacious substance that has just been pricked with a pin. 



" 3rd. Lastly, when we watch the contraction of the vesicula in a recently 

 encysted Vorticella, we observe that at the same moment that it contracts 

 the buccal cavity becomes filled with fluid, and, further, that this fluid dis- 

 appears from the buccal canity, and all trace of the latter "uith it, long before 

 the vesicula reappears, — thus proving at once that the fluid comes from the 

 vesicula, and does not return to it, whatever may become of it afterwards. 



" The position of this organ, then, its manner of contracting, and the buccal 

 cavity of encysted Vorticella becoming filled with fluid the moment it disap- 

 pears (where we know it to be attached to the buccal cavity, and not to the 

 peUieula), are almost conclusive of its excretory office." 



Adopting SpaUanzani's observation (which, however, wants confirmation to 

 estabhsh it as the rule) that the fusiform sinuses of Paramecium Aurelia be- 

 come empty as the vesicle fills, and do not reappear until some time after it 

 has contracted, he infers " that the fluid with which the vesicula is distended 

 comes through the sinuses, but is not returned by them to the body of the 

 Paramecium^ 



'■'■ Xow ia some cases," he continues, " faint hyaline or transparent lines 

 may be seen to extend outwards from each of these sinuses, which Hnes, 

 Eckhard has stated, ' traverse the body in a stellate manner.' Hence, w^hen 

 we add Eckhard's evidence (which I have been able to confirm in a way that 

 will be presently described) to the observation of SpaUanzani, and connect 

 this with the facts abeady adduced in favour of the excretory office of the 

 vesicula, it does not seem unreasonable to conclude that the whole together 

 forms an excretory vascular system, in which the vesicula is the chief recep- 

 tacle and organ of expulsion. 



** While watching Paramecium Aurelia, I on several occasions not only ob- 

 served that the vesiculae were respectively suiTounded by from seven to 

 twelve pyriform sinuses of different sizes, and that lines extended outwards 

 from them in the manner described by Eckhard, but I further observed that 

 these lines were composed of a series of pyiiform or fusiform sinuses, which 

 diminished in size outwards ; and frequently I could trace as many as three 

 in succession, including the one next the vesicula. Hence I am inclined to 

 infer that this vascular system throughout is more or less composed of chains 

 of such sinuses, and that aU have more or less contractile power like that of 

 the vesicula. Just preceding death, when Paramecium A^irelia is compressed. 



