REGULATION IN VORTICELLA. 



E. M. RUNYAN AND H. B. TORREY. 

 (From the Department of Biology, Reed College, Portland, Oregon.) 



It is a fact well known to students of regeneration that one 

 part of an organism may exert a measurable influence over the 

 growth and development of another. This has been demon- 

 strated for many of the Metazoa under varying forms. The 

 removal of the head of a planarian liberates, as it were, the post- 

 jacent tissue, out of which a new head is fashioned. Among 

 macruran crustaceans, the loss of the larger chela of an asym- 

 metrical pair has been shown many times to be succeeded by an 

 accelerated growth of the smaller chela and a subsequent retarda- 

 tion in the regeneration of the lost chela so that, in the presence 

 of the small chela grown large, it remains the smaller of the two. 

 Finally not to multiply instances needlessly when a short 

 length of the column, with hydranth, is cut away from the hydroid 

 Corymorpha, no development beyond closure of the wound occurs 

 proximally until the hydranth is removed from the distal end. 

 In this respect, the behavior of Corymorpha may be contrasted 

 with the behavior of the planarian, since in the latter the presence 

 of the original head on the anterior piece does not inhibit the 

 development of a tail posteriorly. The hydranth in Corymorpha 

 appears somehow to inhibit, in short pieces, even the development 

 normally to be expected at the aboral end. 



Among the Protozoa, instances of this last sort seem so gen- 

 erally to have escaped record, that we have thought it desirable 

 to describe a similar domination in Vorticella sp. of one part over 

 another. 



When Vorticella divides, the fission plane passes approxi- 

 mately through the center of the organism from oral disk to a 

 point immediately to one side of the contractile stalk. Of the 

 zooids thus formed, one remains attached to the original stalk, 

 while the other swims away by means of cilia which, during the 



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