206 JELLY-FISH, STAR-FISII, AND SEA-UKCHINS. 



interesting character to describe, which is closely 

 connected with the current views respecting gan- 

 glionic action, and may therefore be more con- 

 veniently considered here than in any other part of 

 this treatise. I have already stated that in no case 

 is the manubrium of a Medusa affected as to its 

 movements by removal of the periphery of the 

 swimming-bell ; but in the case of Sarsia a very 

 interestino- chancre occurs in the manubrium soon 

 after the nectocal^^x has been paralyzed by excision 

 of its margin. Unlike the manubriums of most of 

 the other Medusce, this organ, in the case of Sarsia, 

 is very highly retractile. In fresh and lively speci- 

 mens the appendage in question is carried in its 

 retracted state ; but when the animals become less 

 vigorous — from the warmth or impurity of the 

 water in which they are confined, or from any 

 other cause — their manubriums usually become 

 relaxed. The relaxation may show itself in various 

 degrees in different specimens subjected to the same 

 conditions, but in no case is the degree of relaxa- 

 tion so remarkable as that which may be caused 

 by removing the periphery of the nectocalyx. For 

 the purpose of showing this effect, it does not 

 signify in what condition as to vigour, etc., the 

 specimen chosen happens to be in ; for whether 

 the manubrium prior to the operation be contracted 

 or partially relaxed, within half an hour after the 

 operation it is sure to become lengthened to a 

 considerable extent. 



In order to shovv^ the surprising degree to which 

 this relaxation mr.y proceed, I insert a sketch of a 



