xxxn LETTERS TO MARCO 213 



to arrest the speed, though it cannot be used 

 for backing, as the pectoral fins of the fish. 



In my sketch of a jack you will notice how 

 very large the dorsal and anal fins are. They 

 are set far back, close to the tail, and, taken 

 together, form almost a second large tail. I 

 have no doubt they give an enormous assist- 

 ance to the propelling power, making the rush 



Sketch of a Jack. 



forward extremely rapid. In most fishes 

 these two fins serve chiefly as keels to steady 

 the fish. The pectoral and centre fins no 

 doubt do the steering. All these fins can be 

 closed or expanded at will. 



A pair of swans have this year taken up 

 their quarters in front of our house. They 

 are young birds, probably driven away from 

 their birthplace by their parents. They are 

 very much in love with one another at 



