60 PHYSIOGNOMY OF PLANTS. 



atmosphere that the light-evolving auimalculse come in large 

 numbers to the surface of the sea. It has been asked why 

 the fresh water of our marshes, which is filled with polypi, 

 is never seen to become luminous. Both in animals and 

 plants, a particular mixture of organic particles appears to 

 be required in order to favour the production of light. 

 "Willow-wood is oftener found to be luminous than oak-wood. 

 In England experiments have succeeded in making salt- 

 water shine by pouring into it the liquor from pickled 

 herrings. It is easy to shew by galvanic experiments that 

 in living animals the evolution of light depends on an irri- 

 tation of the nerves. I have seen an Eiater noctilucus 

 which was dying emit strong flashes of light when I touched 

 the ganglion of his fore leg with zinc and silver. Medusae 

 sometimes shew increased brightness at the moment of 

 completing the galvanic circuit. (Humboldt, Eelat. Hist. 

 T. i. p. 79 and 533.) 



Respecting the wonderful development of mass and power 

 of increase in Infusoria, see Ehrenberg, Infus. S. xiii. 291 

 and 512. He observes that "the galaxy of the minutest 

 organisms passes through the genera of Vibrio and Bac- 

 terium and that of Monas, (in the latter they are often 

 on ty ToVo f a une >) S. xix. and 244. 



( 6 ) p. 7. " Which inhabits the large pulmonary cells of 

 the rattle-snake of the tropics." 



. This animal, which I formerly called an Echinorhynchus 

 or even a Porocephalus, appears on closer investigation, and 

 according to the better founded judgment of Rudolphi, to 



