FUNDAMENTAL RELATIONS OF ANIMALS 91 



capable of controlling all these external influences, as well as regu- 

 lating the course of life of every being, and establishing it upon such 

 an immutable foundation within its cycle of changes, that the un- 

 interrupted action of these agents does not interfere with the regular 

 order of their natural existence? 



There is, however, still another conclusion to be drawn from these 

 facts: they point distinctly at a discriminating knowledge of time 

 and space, at an appreciation of the relative value of unequal amounts 

 of time and an unequal repartition of small, unequal periods over 

 longer periods, which can only be the attribute of a thinking being. 



SECTION XX 

 ALTERNATE GENERATIONS 



While some animals go on developing gradually from the first 

 formation of their germ to the natural end of their life and bring 

 forth, generation after generation, a progeny which runs with never 

 varying regularity through the same course, there are others Avhich 

 multiply in various ways, by division and by budding, or by a strange 

 succession of generations, differing one from the other, and not re- 

 turning by a direct course to their typical cycle. 



The facts which have led to the knowledge of the phenomena now 

 generally known under the name of alternate generation were first 

 observed by Chamisso and Sars, and afterwards presented in a 

 methodical connection by Steenstrup, in his famous pamphlet on 

 that subject. ^^^ As a brief account of the facts may be found in almost 

 every text-book of Physiology, I need not repeat them here, but only 

 refer to the original investigations in which all the details known 

 upon this subject may be found. These facts show, in the first place 

 with regard to Hydroid Medusas, that the individuals born from eggs, 

 may be entirely different from those which produced the eggs, and 

 end their life without ever undergoing themselves such changes as 



"'Ludovici A. de Chamisso, De animalibus quibusdam e classe Vermium Linneana 

 (Berlin, 1819); Michael Sars, Beskrivelser og Jagttagelser over nogle maerkelige eller 

 nye i Havet ved den Bergenske Kyst levende Dyr . . . (Bergen, 1835); Johann Steen- 

 strup, Ueber den Generations-Wechsel oder die Fortpflanzung und Entwickelung durch 

 abwechselnde Generationen . . . (Copenhagen, 1842). 



