G. GENERAL NATURAL HISTORY AND ZOOLOGY. 259 



finds a great resemblance between this Kansas fauna and 

 that of the English chalk, no less than six of the eight Kan- 

 sas genera having been found in the latter. 2 D, MSS., Feb- 

 ruary 2 , 1*1 2. 



USE OP THE PECTORAL FINS OF FISH. 



Mr. Hansen, in discussing the movements of the fins of 

 fishes in water, remarks that the propelling power of the 

 pectoral fin is directed upward and forward, and is intended 

 to assist the passage of the water into and out of the gills, 

 and thus aid in respiration. When only one pectoral fin is 

 moved, the body rotates around its longitudinal axis ; a more 

 decided movement of both fins will raise the anterior extrem- 

 ity of the body in the water. When flying-fish ascend quick- 

 ly to the surface by means of the active movement of the 

 pectoral fins, they describe an arc over the water, but ulti- 

 mately fill back into it. For this reason they are scarcely 

 to be included among flying animals. 1 C\ 1870, xlv., 720. 



NEST-BUILDING FISH. 



The first contribution to science from the Sassier expedi- 

 tion, under Professor Agassiz, appears in the form of a letter 

 addressed to Professor Peirce, dated St. Thomas, December 

 15. In this it is stated that, in the course of the frequent ex- 

 amination of the floating Gulf-weeds, made daily, for the pur- 

 pose of collecting the marine animals that usually inhabit 

 them, a mass of this weed was found, the branches and leaves 

 of which were united together by fine threads, wrapping it 

 in every direction into the form of a ball. The threads form- 

 ing the connecting material were elastic, and beaded at in- 

 tervals ; the beads being sometimes close together, sometimes 

 more remote, a bunch of them occasionally hanging from the 

 same cluster of the threads. From the accounts of the pro- 

 fessor it would appear as if a globular mass had been formed 

 by wrapping up a small quantity in the thread, and then 

 adding more, and continually wrapping it up, until a ball of 

 considerable size was produced. 



A careful examination of these beads showed that they 

 were in reality the eggs contained in the substance of the 

 threads, and in some the embryo was sufficiently far advanced 

 to prove that they belonged to a fish. The mass was pre- 



