240 ANIMAL SKETCHES. CHAP. 



have pried deeply enough into the inwards of this little 

 fish. There are disadvantages in too great transparency, 

 whether of mind or of body, in men and eels. But before 

 I return my little elver to comparative freedom in the 

 aquarium tank, I must just for one moment place his 

 transparent tail under the higher power of the compound 

 microscope. He does not approve of this treatment, and 

 struggles to be free. But there he is ; and we can take a 

 rapid glance while he is still. We see embedded in the 

 skin the star-shaped blackish pigment spots spreading 

 widely beneath the surface, and combining with the sur- 

 rounding white to give the grey tint to the elver. Deeper 

 down we see clearly marked out the vertebrae of the tail, 

 and above them the spinal marrow. We see, too, the 

 delicate soft rays which run out in and support the fringing 

 tail-fin. But what is that which makes the whole seem 

 a-dance with life ? It is the blood that is being pumped 

 through the tiny vessels by the heart, which we saw pul- 

 sating behind the gills. Beneath the end of the backbone 

 we see two vessels. In one the blood is running down- 

 wards towards the tail, and breaks up into little vessels 

 proceeding outwards in the fin parallel to its supporting 

 rays. In the other the blood is moving forwards on its 

 way back to the heart. It is supplied by little vessels also 

 running parallel to the rays in the fin ; and if we watch 

 carefully near the edge of the fin, we can see the blood- 

 discs hurried round from the outward-going to the inward- 

 coming vessels. 



Under the influence of our treatment our poor little fish 

 has gone quite pale ; and the microscope shows that the 

 pigment stars are much more contracted, less spread out 

 than they were, so that the skin has a more dotted appear- 

 ance. We must not longer try his patience, his temper, 

 and his constitution. He has gulped a great globule of 



