( 177 ) 

 ORIGINAL COMMUNICATIONS. 



On ^Ae Occurrence among the Infusorfa of peculiar Organs 

 resemhlinq Thread-cells. By George J. Allman, M.D., 

 F.R.S. (With a Plate.) 



(Read at the Meeting of the British Association at Liverpool, Sept. 1854.) 



In an important monograph by Cohn on the Paramoecium 

 Bursaria,* tliis author maintains that the cilia with which the 

 whole surface of the animalculae is covered are in reality much 

 longer tlian their appearance in the living animal would lead 

 one to believe. He founds this opinion on the fact, that 

 when the animal is allowed to dry on the glass object-holder 

 it is seen to bristle with long rigid filaments, which he be- 

 lieves to be the cilia, really unaltered in length, though then 

 for the first time become visible in their entire course ; and, 

 in accordance with this view, he figures the Parama'cium 

 covered with cilia very much longer than the inspection of 

 the living animal alone would justify. 



Stein, in his remarkable work on the development of the 

 Infusoria,! refers to this opinion of Cohn, whom, however, he 

 considers in error, in supposing the long bristle-like pro- 

 cesses of the dead animalcule to represent the natural length 

 of the cilia in the living. He maintains on the contrary that 

 these processes are the cilia abnormally lengthened under ex- 

 ternal influences ; and he states that he has witnessed the 

 same phenomenon in many other Infusoria in which he has 

 always been able to induce it by the application of strong 

 acetic acid, when the cilia suddenly extend themselves to 

 three or four times their original length. 



While recently engaged in examining the structure of a 

 nearly allied animalcule, the Bursaria leucas, Ehr. — a green 

 variety of which was developed during the present autumn in 

 great profusion in a small pond in the county of Essex — I 

 witnessed an appearance exactly similar to that described by 

 Cohn and Stein ; but it soon iDecame clear to me that the 

 German naturalists had erred in their explanations of it ; and 

 I am now satisfied that the filaments in question have nothing 

 whatever to do with the cilia, but are peculiar and very re- 

 markable organs, hitherto undescribed in the Infusoria. 



When this animalcule is examined under a sufficiently 



* Siebold u. Kolliker Zeitschrift. Bund III. 260. 



t Die Infusionsthiere auf ihre Entwickelungs geschichte. (' Quarterly 

 Journal of Microscopical Science,' Vol. ii., p. 272. 



VOL. III. N 



