G. NATURAL HISTORY AND ZOOLOGY. 349 



4, the compression of the bladder by muscular action upon 

 it this was, however, seldom observed, and was very slight. 

 Upon the whole, the bladder seems to play almost no active 

 part in the upward and downward movements of fish in wa- 

 ter. The experiments were, however confined to fresh-wa- 

 ter fish. 19 C, July 11, 1874, 271. 



> 



THE DEVELOPMENT OF SHARKS AND RAYS. 



Mr. F. M. Balfour, who was engaged in the summer of 

 1874 at the zoological station at Naples in investigating the 

 development of the sharks and rays, announces to the British 

 Association, as among the results attained, that, although as 

 large a quantity of food-yolk is present in the egg of the 

 shark as in that of a bird, there is found in the former a fine 

 network of lines throughout; and around the germinal disk 

 especially there are a number of nuclei. From the presence 

 of these lines, and the nuclei, he concludes that the whole of 

 the yolk, including both the germinal disk and the food-yolk 

 may be looked upon as a single body the ovum in the 

 greater part of which passive food - yolk granules are em- 

 bodied. 



In regard to the mode in which this alimentary canal is 

 formed, the shark is intermediate in condition between the 

 frog and the bird, traces of the primitive mode of formation 

 of the alimentary canal by an involution being retained in 

 the shark, although lost in the bird. 



Mr. Ray Lankester pointed out the very great importance 

 of the discovery that the spinal rod, or notochord, develops 

 in the sharks from one of the two primary layers of the germ, 

 and not from a middle layer, as in the chick or frog. He 

 thought the middle layer would have to be abandoned as 

 an entity, and its elements traced to the outer and inner lay- 

 ers. 15 A, August 29, 1874, 279. 



DEVELOPMENT OF THE EYE IN THE CUTTLE-FISH. 



Mr. E. Ray Lankester has published an account of his ob- 

 servations upon the development of the eye in the cuttle- 

 fish, in which he shows the radical difference in this respect 

 from that of the vertebrates. In .Loligo and Sepia the eye 

 originates as a raised elliptical wall on the surface of the 

 embryo. The wall closes in above, and thus the primary 



