182 AN EXA3IINATI0N OF THE 



Fig. 4. — Development of one of the Lucernarida : — a, Ciliated free- 

 swimming embryo or "planula." h, Hydra-tuha. c, Hydra- 

 tuba further developed, d, Strobila stage, with the secondary 

 circle of tentacles, c, Hydra-tuha, in which the fission has 

 proceeded still further, and a large number of the segments 

 have been detached to lead an independent existence. /, 

 group of young medusae of the natural size, g, Individual 

 seen from above, showing the bifid lobes of the margin, and 

 the quadrilateral mouth, h, Individual viewed sideways, and 

 showing the proboscis. 



Hn £yamitiation of tbe lEyternal Hir 

 of Maebington* 



By J. H. Kidder, M.D., Surgeon U.S.A. Navy.* 



Plate 19. 



DR. KIDDER has very courteously sent us a copy of this 

 report, consisting of twenty-two closely printed pages and 

 ten Phototype plates. 



The first portion of the work treats of the Chemical Analysis 

 of Air, and it may not be uninteresting if we describe the 

 apparatus employed, which is that devised by Dr. Fox, and which 

 brings " continually fresh quantities of air into intimate contact 

 with a small quantity of very pure water, which is reduced to a 

 minute of subdivision by pulverisation." 



By referring to PI. XIX., Fig. i, it will be seen that the aif 

 and water are comminuted by this device probably as finely as 

 possible, and brought into intimate contact with one another. 

 The air can, moreover, be measured with tolerable accuracy, so 

 that there is good reason to expect to find in the w^ater all of the 

 contained solids which are small enough to pass through the jet 

 of the atomiser, and all of the gases and salts which are soluble 

 in water. 



* Extracted from the Report of Surgeon-General P. L. Wales, U.S. Navy, 

 for i88q. — Washington : Government Printing Office, 1882. 



