

BY R. VON LENDENFELD, PH.D. 637 



high development of the muscle in the Ccelenterata mentioned 

 above, has as yet been described of the Hydroid-Polyps. I have 

 however, been enabled to prove that such structures also occur in 

 these least developed forms of all Cnidaria. The Hydro icl -Polyps 

 which produce the Sarsia radiata, V. Lendenfeld, have the peculiar 

 habit of bending themselves down at a joint situated at the base of 

 the Hydranth between it and the top of the Perisarc tube which 

 surrounds the Hydrocaulus. This movement is executed with such 

 precision and rapidity, that I was led to believe that there must be 

 a special organ adapted for this purpose. 



The Perisarc -tube of the Hydrocaulus terminates oblicpdy so 

 that the margin has the shape of an oblique ellipse. In longi- 

 tudinal and transverse sections even with a low power a bundle of 

 longitudinal fibres can be detected, which is 0"5 mm. long and 

 spindle-shaped. It covers that part of the supporting lamella which 

 lays on the side of the Hydranths towards which it bends round. 

 As well by means of osmic acid as by the application of warm 

 solution of corosive sublimate (1) it is easy to kill the Polyps 

 in different positions. If the re-agent does not act quickly, if it 

 is too weak when it reaches the Hydranth, the latter always 

 shuts up entirely and is fixed in this position. Bent down half 

 the Polyps are never fixed, but it is very easy to harden the 

 Polyps in an upright position. This muscle which I name 

 Flexor is peculiar to Sarsia radiata, and no similar structure has, 

 as far as I know, ever been observed in Hydroid-Potyps. We 

 shall see that the histological structure is very different from 

 the ordinary occurrence in the Hydro-Polyps. This structure 

 reminds us of the complicated muscles of the free swimming 



(1) A. Wdssman, Die Entstehung der Sexuazellen bei den Hydro 

 medusen. Iena., 18S3, Seite 13. 

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