PEESIDENTIAL ADDEESS. 5 



will taste that cup of delight, the sweetness of whose 

 draught those only who have made a discovery know." 

 In studying the distribution of animal life in the sea, 

 Forbes recognized several "zones of depth," each charac- 

 terized by particular types of animals — as littoral zone, 

 laminarian zone, coralline zone, and deep-sea coral zone. 

 But on account of the gradual paucity of life as depth 

 increased, Forbes placed the zero of animal life at about 

 300 fathoms, concluding that no life could exist at greater 

 depths. It remained for the "Challenger" Expedition, 

 many years afterwards, to show that ocean depths are not 

 barren solitudes, but the abode of innumerable remarkable 

 forms of life. 



Forbes did more than any man of his day to diffuse 

 abroad a love for natural history, one of his chief aims 

 being to elucidate the past organic history of the earth 

 from a knowledge of its present living forms. He loved 

 to call himself a zoo-geologist. Among his many published 

 writings, his "History of British Starfishes," "A Mono- 

 graph of the British Naked-Eyed Medusae," and with 

 Hanley, the "Handbook of British Mollusca," are still 

 standard works with naturalists. The goal of his ambition 

 was reached (in 1854) when he received the appointment 

 of Professor of Natural History in Edinburgh University, 

 which, however, he lived but a few months to enjoy. 



In 1842, Steenstrup, of Copenhagen, published a 

 remarkable work " On the Alternation of Generations," 

 showing that many species of animals are represented by 

 two perfectly distinct types or broods, differing from each 

 other in form, structure, and habits. The now well- 

 known phenomenon may be particularly well observed 

 among the Zoophytes and the Medusae. 



In 1844 a very remarkable book appeared, entitled the 

 "Vestiges of the Natural History of Creation," the 



