J^' Mr. H. J. Carter on the Organization of Infusoria. 



and Planaria, I am ignorant ; but in some Rotifera (e. g. Bra- 

 chionus Pala, Ehr.) they present themselves at an early period 

 in a circular or discoid group, attached to the cell-wall, and thus, 

 with the absence of the nucleus, closely resemble a granulated 

 state of that organ. 



Vesicula. — I would propose this name for the " Contracting 

 Vesicle,^' on account of the latter being a loose and inconvenient 

 term in description (figs. 3 c, 4 ^). It is certainly the most 

 striking organ of the Infusoria, from its defined circular outline 

 when distended, its hyaline aspect, and above all its sudden 

 disappearance and gradual return at intervals, which give it a 

 pulsatory character, so like that of a heart, that at first we are 

 inclined to conclude that it must be the representative of this 

 organ in the Infusoria. Spallanzani considered it a respira- 

 tory organ* ; Ehrenberg the male organ of generation f; and 

 Siebold a circulatory organ J. The following facts, howevei) 

 would seem to show that it is neither of these, but an excretdi^ 

 organ, viz. : — ''^'^ ,''')if;>il 



1st. It is always seen either close to the pellicula, or close to' 

 the buccal cavity, and always stationary. Thus, in Paramecium 

 aurelittj it is close to the surface, and although it of course passes 

 out of view as the animalcule turns on its long axis, yet it 

 always reappears, after contraction, in the same place (figs. 68 a «, 

 74^ f f) ; while in Vorticella it is attached to the buccal cavity, 

 and, being centrically situated, seldom passes out of view, except 

 when it disappears under contraction, after which it also re* 

 appears in the same place. '.*• 



2nd. In Actinophrys Sol^, and other Amoebce, 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 

 (fig. 24, a). 



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 disappears from the buccal 

 cavity, and all trace of the latter with 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 (fig. 78). 



The position of this organ, then, its manner of contracting, 



• Ap. Dujardin, op. cit. pp. 103, 104. f Idem, pp. 105-108. 



X Ap. Claparede, Ann. & Mag. Nat. Hist. vol. xv. p. 212, 1855. 

 § Idem, loc. cit. pi. viii. fig. 1. 



