WESTWOODIA. 



C 817 ] 



WHALEBONE. 



tiaceous Mosses, variouslydefined by authors, 

 related to Gt/mnosfomum. W. controversa 

 (W. viridula, Miill.) is common on banks. 

 Wilson includes Blindia here, and separates 

 W. fuyux and denticulata as Rhabdoiveissia. 

 (W'ilmn, Bn/ol. Br. 4Q.) 



WESTWOODIA, Dana, = Arpadicus 

 pt. W.nobilis = Arp.nob.jXn.'AY\)iQ. (Bradv, 

 Copep. ii. 140.) 



WILALEBONE.— In whales the teeth 

 are rudimentary ; and arising from a depres- 

 sion ill the upper jaw on each side are a 

 number of parallel horny plates, many feet 

 in length, which proj ect downwards : these 

 plates, which are technically known as fins 

 or blades, constitute whalebone ; and through 

 them the water containing the animals upon 

 which the whale hves is strained, and the 

 food thus obtained. These plates are situ- 

 ated upon a vascidar membrane, folds of 

 which enter a cavity at their base, which is 

 the portion connected with the jaw. 



Whalebone may be pretty easily divided 

 into longitudinal laminae and fibres ; but 

 these are oulj^ secondary forms resulting 

 fi'om the aggregation of a number of cells 

 of which whalebone wholly consists. 



On examining a transverse section of a 

 blade or plate of whalebone with the naked 

 eye, or a lens, two structures are readily 

 distinguishable — an inner porous-looMng 

 medullary portion, surrounded by an outer 

 compact or cortical substance. A longitu- 

 dinal section through the plate exhibits a 

 number of dark lines or stripes, fi-om about 

 1-100 to 1-150" in diameter, parallel to each 

 other and to the axis of the plate, and cor- 

 responding to the pores seen in the trans- 

 verse section. These stripes, which have 

 been called whalebone-canals, but which we 

 shall denominate medullary lines, are seen 

 to be sun-oimded by a paler substance. 



With a higher power {\ inch), the trans- 

 verse section exhibits in the centre a num- 

 ber of rounded apertures or circles con-e- 

 spondiug to the pores (PL 22. fig. 31), sui-- 

 rouudedby very tine, concentric, interrupted 

 dark lines, whilst towards the cii'cumfer- 

 ence these lines run parallel to the surface 

 of the plate. In the longitudinal section, 

 viewed with this power, the medullary lines 

 are seen to consist of a number of cells 

 (PI. 22. fig. 30), mostly arranged in single 

 longitudinal series, and, in dried whalebone, 

 having a very dark appearance by trans- 

 mitted light, from the presence within 

 them of a large quantity of pigment and 

 air. These are the medullary cells. The 



sing them 



iug a transverse section 



substance between the lines of medullary 

 cells exhibits very fine longitudinal strise, 

 and, in parts, the ends of divided laminae. 



On macerating whalebone for twenty- 

 four hours in solution of caustic potash, it 

 becomes soft ; and on aftei-wards digesting 

 it in water, the cortical portion resolves 

 itself into numerous large transparent cells 

 from 1-230 to 1-310" in length, and fi-om 

 1-500 to 1-330" in breadth (PI. 22. fig. 33). 

 These contain a variable number of gra- 

 nules of pigment, of a deep brown colour, 

 also some small globules of fat, which are 

 especially numerous in those portions near- 

 est the base of the plate. These cells in the 

 natural whalebone are laterally compressed 

 or flattened : and the transverse axes of 

 those surrounding the medullary lines are 

 arranged tangentially to the latter, whilst 

 in the cortical portions these axes are par- 

 allel to the surface of the plate. The con- 

 centric lines seen in a transverse section 

 arise principally from the pigment-granules 

 within those cells which sui'round the me- 

 dullary cells becoming arranged in a linear 

 series by the flattening of the cells enclo- 

 This may be shown by treat- 

 of whalebone with 

 caustic potash, and then adding water and 

 watching its resolution into cells. As these 

 expand, the interrupted lines are seen also 

 to expand as it were, and to become re- 

 solved into a number of distinct pigmenl- 

 grauules existing within each cell. The 

 lines seen in a longitudinal section arise 

 from the miequal refraction of light by the 

 laminae of compressed cells surrounding the 

 medullary lines. 



The medullary cells contain a large quan- 

 tity of pigment, as do also those compressed 

 cells which immediately surround them ; in 

 the former these grauides are frequently 

 aggregated. In the common dry whale- 

 bone of commerce the medullary cells also 

 contain air, which has been mistaken for 

 fat, and hence the cells denominated fat- 

 cells. The air is readily displaced by liquids. 

 Between the compressed ceUs, minute ca- 

 vities containing air, sometimes assuming a 

 linear form, at others representing mere 

 dots, are seen both in the transverse and 

 longitudinal sections ; these are distin- 

 guished by the displacement of their con- 

 tents. Hence ordinary whalebone closely 

 resembles hair or horn in its structure ; and 

 the fibres which are seen projecting from 

 the margin of the blades as found in com- 

 merce have a remarkable similarity to hair 



3g 



