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XX. — On the Occurrence of Parasitic Rotifera in Volvox globator. 

 By Mr. John Williams, Assistant Secretary. 



(Read June 26, 1850). 



Ehrenberg, in his fourth figure of Volvox globator, represents one 

 having within it a parasitic Rotifer, which he calls Notomata petro- 

 myzon ; and in his fiftieth plate, describing Notomata parasita, he 

 figures the same as occurring within Volvox globator. With these ex- 

 ceptions, I have not hitherto met with any account or figure of para- 

 sites within that animalcule, and as a case occurred to me since the 

 last meeting, I am induced to lay an account of it before the Society, 

 considering, that although these appearances have been observed 

 before, still, as they are comparatively of rare occurrence, a well- 

 authenticated observation of so extraordinary a fact might be of 

 some value, as well as of interest to the members of the Society. 



At the meeting of June the 12th I was supplied, by the kindness 

 of Mr. Rosling and Mr. Ingpen, with some water containing nu- 

 merous specimens of Volvox globator. The next evening, on 

 examining some of these in a live-box, my attention was drawn to 

 one of considerable size, within which appeared a large animalcule 

 moving about with much activity, having the appearance of one of 

 the Rotifera, and which I have no doubt was Notomata parasita. In 

 length it was about one-third of the diameter of the Volvox, and its 

 breadth might be about one-eighth. The Volvox presented the 

 usual granular green spots, with five of those larger agglomerations 

 of granules commonly seen in this creature. It was evidently living, 

 as it not only moved about in the usual manner, but small bodies 

 which came near to its edge were driven away with great velocity. 

 There was also within it a fixed mass of gelatinous matter of irregu- 

 lar shape, in which at times I fancied I saw ciliary movements, but 

 they were so indefinite, that I was by no means certain of the fact ; 

 in other respects this mass was perfectly motionless. As these ap- 

 pearances seemed to be something unusual, I was careful not to dis- 

 turb the arrangement, and left everything as it was until the next 



TRANS. MIC. SOC. VOL. III. S 



