44 8 ANIMAL RESPIRATION 



creature is able to make its way through damp herbage for con- 

 siderable distances, the object apparently being migration from 

 one pond or river to another. In correlation with this habit the 

 external breathing aperture is narrowed somewhat as in a mud- 

 skipper (see below), though most likely this character was first 

 acquired to hinder mud from making its way into the gill-cavity 

 and blocking up the gills. 



Carp and their allies are often extremely tenacious of life, 

 some of them being able to thrive in stagnant water, and others 

 to endure exposure to the air for a considerable time, provided 

 it be not too dry. Regarding the Common Carp (Cyprinus 

 carpio], Giinther remarks (in The Stiidy of Fishes]'. " They 

 can also be preserved alive for a considerable length of time out 

 of the water, especially if care be taken to moisten them occa- 

 sionally as they become dry. Advantage is often taken of this 

 circumstance to transport them alive, by packing them among 

 damp herbage or damp linen; and the operation is said to be 

 unattended with any risk to the animal, especially if the pre- 

 caution be taken to put a piece of bread in its mouth steeped in 

 brandy!" The Tench (Tinea vulgaris) can live in stagnant water 

 of so foul a nature as to be fatal to most other fishes, which 

 suggests that it probably makes up for the deficiency of oxygen 

 by rising to the surface to take in air. 



Cases like those just described lead on to others where the 

 term amphibious is correctly applied. The most striking marine 

 forms of this kind are the little Mud-Skippers (Periophthalmus], 

 which hunt for small crustaceans and the like between tide-marks 

 on the shores of the I ndo- Pacific (see p. 87). To prevent the 

 gills from drying up at such times the external opening behind 

 the gill-cover is not a wide slit as in, say, a herring or perch, 

 but has been reduced to a comparatively small hole. It also 

 appears that the gill-cavity is relatively spacious, and most pro- 

 bably its lining performs the functions of a lung. Another very 

 interesting fact concerning the breathing of these fishes is thus 

 described by Hickson (in A Naturalist in Celebes]'. " Their 

 position is usually one of clinging to the edge of the rocks or 

 mangrove roots by their fins, with their tails only in the water. 

 . . . The fact that they live the greater part of their lives with 

 their head and gills out of water suggested to me an investigation 

 of their respiratory organs, as I thought it possible that they 



