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clear expositions and enlightened discussions of truths already 

 known, but is enriched throughout with the fruits of the author's 

 own observation and experimental inquiry. Evidence of this may 

 be found in almost every chapter, but it is sufficient to refer to his 

 examination of the blood, to his disquisitions on the nervous system, 

 and especially to his valuable experimental investigations on the 

 voice and on hearing. 



Professor Muller early applied himself to the study of the struc- 

 ture and economy of the Echinoderms. After describing, in a 

 special memoir, the anatomy of the Pentacrinus, so interesting as a 

 living representative of the extinct Crinoidea, and publishing, in 

 conjunction with M. Troschel, a systematic arrangement and de- 

 scription of the Asterida, he was at length happily led to investigate 

 the embryo life of this remarkable class of animals. The field of 

 inquiry on which he entered had scarcely been trenched upon be- 

 fore, and he has since made it almost wholly his own by persevering 

 researches carried on at the proper seasons for the last nine years, 

 on the shores of the North Sea, the Mediterranean and the Adriatic. 

 In this way he has investigated the larval conditions of four out of 

 the five orders of true Echinoderms, and has successfully sought out 

 and determined the common plan followed in their development, 

 amidst remarkable and unlooked-for deviations in the larval organi- 

 zation and habits of genera even of the same order ; and his inqui- 

 ries respecting these animals have made us acquainted with larval 

 forms, with relations between the larva and future being, and with 

 modes of existence, such as nature has not yet been found to present 

 in any other part of the animal kingdom. Finally, with the light thus 

 derived from the study of their development, Professor Muller has 

 subjected the organization of the entire class of Echinoderms, both 

 recent and fossil, to a thorough revision, and has added much that 

 is new, as well as cleared up much that was obscure, in regard to 

 their economy, structure and homologies. It is to these researches, 

 which occupy seven memoirs in the Transactions of the Royal Aca- 

 demy of Sciences of Berlin, that more special reference is made in 

 the award of the Medal. Besides their other claims to distinction, 

 they may be justly regarded as revealing a new order of facts in the 

 history of animal development. 



