REVIEWS — THE GENETIC CYCLE IN ORGANIC NATURE. 515 



warmer than that below, and consequently would rather tend to make 

 it float. Its only use, therefore, must be to compress the air. If it 

 was intended that the bird should use the same means to alter its 

 specific gravity, would it not be provided with some special apparatus, 

 as we see the Nautilus is ? No such provision, however, nor the most 

 distant approach to it, exists in the bird ; but its external surface is 

 capable of great compression, and is abundantly furnished with power- 

 ful muscles, the combined action of which would be to compress the 

 body, and they are under the control of the will of the bird. With 

 the knowledge of all these facts before me, I can come to no other 

 conclusion than that the bird does so compress its body as to con- 

 dense the air in its various cavities to such an extent as to render the 

 specific gravity of its body about the same as that of the water in 

 which it swims. 



REVIEWS 



The Genetic Cycle in Organic Nature ; or, the Succession of Forms in 

 the Propagation of Plants and Animals. By George Ogilvie, M.D., 

 Regius Professor of the Institutes of Medicine in the University of 

 Aberdeen ; author of "The Master Builder's Plan in the Typical 

 Forms of Animals." Aberdeen : A. Brown & Co. Edinburgh : 

 John Menzies. London: Longman & Co. 1861. Crown 8vo, 

 pp. 296. 



In a former volume of this Journal we gave some account of the 

 author's previous work, "The Master Builder's Plan," which is a 

 very pleasing one, fitted for popular use, and perhaps better fitted 

 than any we are acquainted with to give a good general idea of the 

 plan of creation in the animal kingdom. The present volume has 

 been long upon our table, but has always seemed to us to demand 

 more attention than we could at the moment bestow upon it ; and 

 though it'ijhas interested us much, we must now be content with a 

 slight notice, that we may no longer omit to recommend it to 

 physiological inquirers. If decidedly less fitted for popularity than 

 the former work, it has certainly no less claims on the attention of 

 the real student of Nature, and in proportion to the difficulty and 

 Vol. VII. 2 g 



