272 



MOVEMENTS OF THE I'OLLIXIA. 



CUAl-. IX. 



'■?• 



3S. 



I)isc of Gymnadcnia conopsea 



is seen from above liiglily magnifie«l In the upper of 

 the two adjoinino: figures ; and in^the lower figure wo 

 have a longitudinal section of the micontracted disc, 

 together with the base of tlie attached and upright 

 caudicle. At the broad end of the disc there is a deep 

 crescent-shaped depression, bordered by a slight ridge 



formed of lonjiitudinallv elon- 

 gated cells. The end of the 

 caudicle is attaclied to the 

 steep sides of this depressicni 

 and ridge. When the disc is 

 exposed to the air for about 

 thirty seconds, the ridge con- 

 tracts and sinks flat down ; in 

 sinking, it drags with it the 

 caudicle, Avhich then lies paralhd to the elongated 

 tapering part of the disc. If placed in water the 

 ridge rises, re-elevating the caudicle, and when re- 

 exposed to the air it sinks again, but each time with 

 somewhi^t enfeebled power. During each sinking and 

 rising ef the caudicle, the whole pallinium is of course 

 depressed and elevated. 



That the power of movement lies exclusively in the 

 surface of the disc is well shown in the case of the 

 saddle-shaped disc of Orchis i^yramidalis ; for whilst it 

 Avas held under water I removed the attached caudicles 

 and the layer of viscid matter from the inferior surface, 

 and immediately that the disc was exposed to the air 

 the proper contraction ensued. The disc is formed of 

 several layers of minute cells, which are best seen in 

 specimens that have been kept in spirits of wine, 

 for their contents are thus rendered more opaque. The 

 cells in the flaps of the saddle are a little elongated. 

 As long as the saddle is kept damp, its upper suriace 

 is nearly flat, but when exposed to the air (see fig. 3, 



