MEMORANDA. 105 



remain. By some microscopists tliey are regarded as por- 

 tions of a water- vascular system — these observers believing 

 that they have found an external opening communicating 

 with the water ; by others they are supposed to form a 

 rudimentary circulating system (heart) ^ by which the liquid 

 produced from the digestion of food is circulated through the 

 body; my o^\\\ 2J7^esent view will be gathered from the follow- 

 ing observations : 



The contractile vesicle I have almost invariably found to 

 be near the surface of the body. 



Glaucoma scintiUans is furnished with 07ie central vesicle, 

 and when that contracts, it forces the fluid into others which 

 appear to be temporarily formed around it ; these in their 

 tm'n amalgamate and form the central vesicle by fusing their 

 contents together. This, I believe, to be the whole circula- 

 tion in the form named, and I do not find in this case that 

 the surrounding vesicles have any outlets or canals as de- 

 scribed by Lieberkiihn. The central vesicle I have almost 

 always found to be on the side furthest removed from the 

 object-lens (the animalcule appears to move in this position), 

 and the auxiliary vesicles are formed imvards — i. e., the fluid 

 rises into the body, and there forms the vesicles. This may 

 be tested by raising the object-lens whilst the central vesicle 

 is contracting, and depressing it when the amalgamation 

 takes place (of the smaller vesicles) . I believe that my ob- 

 servation in this respect is accurate, as I have frequently 

 repeated it, and am therefore somewhat inclined to regard 

 the contractile vesicle as a heart ; that it should be near the 

 surface is natural, and by bringing the nutritive fluid into 

 close contact with the water, it renders the admission of that 

 medium into the body unnecessary. The nutritive fluid seems 

 to alternate between the central and surrounding vesicles. 



In Paratnecium caudatum, a species of Amphileptus, a 

 freed Vorticella, &c. I have frequently and clearly traced 

 the canals that empty themselves into the contractile vesicle. 

 In the second-named species, these canals were very per- 

 ceptible ; they proceeded along the edge of the body where 

 the cilia were the most active (also probably because there 

 the current of fresh water would be constantly renewed) , and 

 at the embouchure into the central vesicle, swelled into a 

 bulb-shape. In the Vorticella, the contractile vesicle had a 

 canal which communicated either with the external surface, 

 through the oral aperture, or passed round the oral wreath. 

 I was inclined to believe the latter to be the case (perhaps 

 my bias may have influenced the observation) . 



