142 BALANID.F-. 



fectly successive layers of cement often become blended 

 together, lines of union or junction, could hardly be ex- 

 pected to be preserved in the same individual layer.- When 

 the circumferential slip of basal membrane splits, the under- 

 lying slip of cement, which we will call a, does not split, 

 but becomes stretched, so that the newly-formed slip of 

 cement, which we will call b, does not reach the skin of 

 the whale. As the new circumferential slip of basal mem- 

 branes goes on increasing in width, a continues to be 

 stretched, but does not split, till at least another circum- 

 ferential slip of basal membrane has been formed and has 

 been split, and till b has been also stretched. By this 

 time, the cement-tissue a has assumed its normal structure, 

 and has the power of adhering to the whale's skin, which it 

 has now reached, owing to the splitting of the under and 

 older slips of cement. At the next period of growth, a 

 itself will split, and b will touch the whale's skin and 

 adhere to it ; and this, also, will ultimately split. It results 

 from this action, that the cement has a stretched, and some- 

 times even a fibrous appearance, with the lower edges of the 

 layers, of which each slip of cement is formed, thinning out. 

 I have before stated, that the two or three last-formed 

 slips of basal membrane are formed at first too narrow, 

 and apparently have to be dragged outwards, over each 

 other ; and it is perhaps owing to this circumstance, and 

 to globules of cement having first adhered to the under 

 surface of the slips of basal membrane, that these slips are 

 studded beneath with parallel little vermiform bodies, some- 

 times of considerable length, and furnished with heads, all 

 directed outwards. These tapering, vermiform bodies have 

 a considerable resemblance to the threads before mentioned, 

 which give the wrinkled, concentric appearance to the 

 newly formed layers of cement, and have probably a closely 

 analogous origin : in one case, indeed, it appeared as if 

 some of these concentric threads were in process of being 

 drawn out at right angles to their original course. Lastly, 

 it should be observed, that as the exterior half of the mem- 

 brane of the circumferential slip, after each splitting, is 

 dragged down, and thus comes to invest the outer surface 

 of the wall of the shell (the wall not being represented 



