254 NATURAL HISTORY OF OUR SHORES 



takes place at once, the effect of part drying being to 

 hasten the process. 



No fish furnishes a better object for the study of the 

 circulation, etc., than does this little thing. It holds to 

 life persistently, and can be easily manipulated. 



Placed in a sunk cell, with a drop of water and a cover- 

 glass, as before mentioned for Perophora, the action of 

 the heart, and the whole plan of circulation, can be seen 

 very plainly, the large, oval blood corpuscles are seen 

 rolling and tumbling over in the rushing stream. 



An allied species is figured and described, which bears 

 close relations to the last, and which is named Cottus 

 quadricornis, and which is said to be nearly as common. 

 The distinction is that in the latter species the gill spines 

 are longer, and the colours brighter, usually shades of red. 



As to this being a separate species I am very sceptical. 

 As to colour, it goes for nothing, as colours change markedly 

 and rapidly in each individual. The longer spines are not 

 a much better character. I believe these are one species. 



Cottus bubalis is shown in Fig. 107. 



Cottus exhibits a peculiar feature. If a living specimen 

 is held on the hand, or even touched with the forefinger 

 and thumb just behind the head, a peculiar vibratory 

 movement is felt. I have sometimes thought that it is 

 electrical, as the sensation is much the same as when fore- 

 finger and thumb are placed on the terminals of a coil when 

 a weak current is passing. I have not tried the galvano- 

 meter on the fish, but this experiment would be worth 

 trying. 



Under stones, but usually at a lower zone, may be found 

 the curious little " Butter-fish " (Centronotus gunellus or 

 Gunellus vulgaris). It is about six inches long, of eellike 

 form, but flattened laterally. The colour is light brown, 

 and it has a series of nine or more large, black spots along 

 the back, each spot bordered with yellow. It belongs 



