618 THE POPULAR SCIENCE MONTHLY. 



The shield is partly a portion of the skeleton, and partly an ossifica- 

 tion of the skin or of the walls of the body. 



The second volume treats entirely of the embryology of the turtle, 

 and is illustrated with thirty-four plates. The egg originates from 

 between the cells of the stroma, and is in itself the animal in the first 

 stages of development. The eggs are laid once a year, and grow a 

 long time before they are fecundated. From the first copulation to 

 the laying, four years elapse, during which time eight copulations 

 take place. The segmentation of the yolk takes place during the 

 passage of the egg through the oviduct. From the segmentation of 

 the yolk to the period of hatching, the egg passes through thirty-one 

 stages of development. 



The third volume of the "Contributions" appeared in 1860, and 

 was devoted to the class of Acalephae, the author treating specially 

 of the order Ctenophoroe. The Ctenophorce Agassiz divided into 

 three suborders : the Eurystomoe^ embracing three families, the Sac- 

 catce, with three families, and the Lobatce, with five families. The 

 fourth volume of the "Contributions," in 1862, concluded the Aca- 

 lephae, treating of the Discophora?, Hydroidoe, and the Homologies of 

 the Radiata. 



Of the more recent labors of Agassiz in connection with the Mu- 

 seum of Comparative Zoology at Cambridge — of which he was the 

 director, and to which, in later years, he devoted his whole attention — 

 it is not necessary to speak. With his journey to Brazil in 1865, and 

 his later expedition from Boston to San Francisco on the United States 

 Coast Survey steamer Hassler in 1872, the public is already sufficiently 

 familiar. His last days were devoted to the cause of education, in the 

 establishment of a school of natural history at Penikese Island. 



Of the man himself but a word is necessary. As a naturalist, 

 Prof. Agassiz was unwearied in his devotion to his favorite pursuits. 

 He worked early and late, often denying to himself the most necessary 

 rest and recreation ; and his remarkably strong constitution sustained 

 him under a strain that would quickly have proved fatal to a man of 

 less vigor. His mind was preeminently great ; gifted with a wonder- 

 fully retentive memory, he combined with it a power of generalization 

 and quick perception that places him next to Cuvier, whose disciple 

 he was, and whom he seemed to imitate. In his methods of investiga- 

 tion he w r as perfectly honest, and, though many might differ from him 

 in his conclusions, none could deny the absolute integrity of his con- 

 victions. In his intercourse with his fellow-men he was extremely 

 affable and genial, and especially so toward the young. With inex- 

 perience he was most patient and painstakiug, never wearying in his 

 efforts to aid. Tolerant of ignorance where associated with modest y, 

 he had but little patience with arrogance and ignorance combined. 

 His students will all bear witness to the unvarying cheerfulness and 

 ready sympathy in him they had learned to look up to as their master. 



