PULMONIGRADE ACALEPHAE. .211 



whole can be spontaneously elongated or slowly 

 withdrawn within the body of the Beroe, where 

 they lie enclosed in two sheaths until again required 

 for use. 



These interior ' sheaths/ which resemble in shape 

 the drone of a bag-pipe, are easily seen, being al- 

 most the only parts which are not perfectly trans- 

 parent. They are whitish in colour, and semi- 

 opaque. (Plate VI. contains a sketch of the Beroe, 

 drawn from nature.) 



I may mention that the paddles, with their comb- 

 like array of cilia, flap successively in regular order 

 from the top to the bottom of each row. This 

 wave-like movement takes place simultaneously in all 

 the rows, when the animal is in full vigour. 



The organs of progression in the Pulmonigrade 

 AcalephaB, as their name imports, bear certain re- 

 semblance to the lungs in respiration. They move 

 by the expansion and contraction of their umbrella - 

 shaped bodies. Graceful and elegant indeed are the 

 motions of these creatures. I have seen small speci- 

 mens about the size of a sixpence, advance, in three 

 springs, from the bottom to the top of a large vase in 

 which they were confined. 



In descending they turn over and allow them- 

 selves to sink gradually as if by their own weight. 



The third division of the Acalephse is termed 

 Physograde. The most common member of this 

 group is the Physalus, so well known to all sailors 



