PHYSIOLOGY OF THE INVERTEBRATA. 309 



co-ordination for a considerable time after spontaneity 

 returns. 



(14) Romanes has ascertained the effects of the following 

 poisons — chloroform, amylic nitrite, caffein, strychnia, mor- 

 phia, curare, veratrium, digitalin, atropin, nicotin, alcohol, 

 and potassium cyanide — upon the Mcdufia\* He has shown 

 that there is a wonderful degree of resemblance between the 

 actions of the above-mentioned poisons on the Mcduscc and 

 on the higher animals. This is a most important discovery, 

 especially " when we remember that in these nerve-poisons 

 we possess so many tests wherewith to ascertain whether 

 nerve-tissue, where it first appears upon the scene of life, 

 presents the same fundamental properties as it does in the 

 higher animals." In fact the primitive nervous tissues of 

 the Mcdiiscc adhere to the rules of toxicology that are followed 

 by nervous tissues in general. " In one respect, indeed, there 

 is a conspicuous and uniform deviation from these rules ; 

 for it lias been observed that in the case of every poison 

 mentioned, more or less complete recovery takes place when 



* Fresh water acts as a deadly poison to the Medusa- ; and brine acts as 

 an anaesthetic. The fresh-water Medusa {Limnocodium Sorh'ii) is even more 

 intolerant of sea water than are the marine species of freshwater; and 

 brine acts as a poison to the fresh-v/ater form. " We have thns a curious 

 set of cross relations. It would appear that a much less jjrofound physio- 

 logical change would be required to transmute a sea-water jellyfish to a 

 jellyfish adapted to inhabit brine, than would be required to enable it to 

 inhabit fresh water. Yet the latter is the direction in which the modifica- 

 tion has taken place, and taken place so completely that the sea water is 

 now more poisonous to the modified species than is the fresh water to the 

 unmodified. There can be no doubt that the modification was gradual — 

 probably brought about by the ancestors of the fresh water Medusa pene- 

 trating higher and higher through the brackish waters of estuaries into the 

 fresh water of rivers — and it would be hard to point to a more remarkable 

 case of profound physiological modification in adaptation to changed con- 

 ditions of life. If an animal so exceedingly intolerant of fresh water as is 

 a marine jellyfish, may yet have all its tissue changed so as to adapt them 

 to thrive in fresh water, and even die after an exposure of one minute to 

 their ancestral element, assuredlj' we can see no reason why any animal in 

 earth or sea or anywhere else may not in time become fitted to change its 

 element." (Romanes.) 



