i8o THE POPULAR SCIENCE MONTHLY. 



extraordinary power of apparently dying and returning to life again. 

 "I found his pulse sink gradually," wrote Dr. Cheyne, his medical at- 

 tendant, " so that I could not feel it by the most exact or nice touch. 

 Dr. Raymond could not detect tiie least motion of the heart, nor Dr. 

 Skrine the least soil of the breath upon the bright mirror held to his 

 mouth. We began to fear that he was actually dead. lie then began 

 to breathe softly." The colonel tried this experiment a number of times 

 during his illness, and was able to render himself insensible at will. 



Dr. Brown-Sequard, in a course of lectures before the Boston- 

 Lowell Institute, last winter, illustrated many like remarkable powers 

 of mind in mental and physical disease, by cases which had come 

 under his own observ^ation. From such cases it would seem that the 

 mind is largely dependent on physical conditions for the exercise of 

 its faculties, and that its strength and most remarkable powers, as 

 well as its apparent weakness, are often most clearly shown and rec- 

 ognized by some inequality of action in periods of disturbed and 

 greatly-impaired liealth. 



-<- 



PEOGRESSION AND RETROGRESSION. 



By Tkof. W. D. gunning. 



WE walk along a rocky beacli when the tide is out. Twice every 

 twenty-four hours this narrow zone is sea and twice it is land. 

 Its tenants are, as itself, a sort of dividing zone between land and 

 sea. The Alga3 in the tide-pools will remind you of Conferva? in the 

 ponds. The littorinje on the rocks will remind you of snails. The 

 shapeless, gelatinous clumps adhering to rocks oi- whai'f-posts will re- 

 mind you of garden slugs, or naked snails. We wdll give our atten- 

 tion first to tliese soft and shapeless chimps. 



They will call up no image in the mind until the sea returns, or 

 until you detach one of them, and drop it into a glass of sea-water. 

 You have a Dendronotus, or a Doris, or an Eolis, or an Aplysia. 



Out of the shapeless chmip comes a form like that of the sing ; 

 but the slug in our captive is soon disguised, for along its back, from 

 end to end, rises a fringe of pinkish papilla?. We have an Eolis. 

 What does Eolis do with these papillae V The last generation of 

 natui-alists said, " He breathes with them." 



The last generation was too sparing of the knife. We cut through 

 Eolis's back till we reach the stomach, which we find to be a mere ex- 

 pansion of the intestinal tube. This tiibe extends lengthwise througl) 

 the body and lies near the dorsal, not the ventral side. It branches, 

 and the branches branch again, and run up into the pa])illa? which 

 stand out like quills on an angry porcupine. The j^apilla? are supple*- 

 mentary stomachs. 



