MELANOPHORE A TYPE OF SMOOTH MUSCLE CELL 209 



AN ANALYSIS OF THE CONTHAC'i^ION IX THE ^na.ANOPHORE 



A structural and functional parallelism between smooth mus- 

 cle and melanophores can scarcely be considered complete with- 

 out a comparison of the contractions in the two cases. At first 

 sight they have little in common. Indeed the exact mechanical 

 nature of the contraction in the melanphores is still a disputed 

 question. Certain facts are established beyond anj^ reasonable 

 doubt viz: 1) the proximal and distal pigment migrations invari- 

 ably occur along fixed paths (Kahn u. Lieben '07, Spaeth '13 b); 

 2) in cases where living cells have been observed under high mag- 

 nifications it has appeared that the pigment granules are not 

 merely carried along passively by a streaming or flowing of an 

 extremely liquid sort of protoplasm, but that the.v exhibit acti\'e, 

 independent movements within the cell processes (Ballowitz 

 '13 a and b, Degner '12). Exactly what occurs after the pig- 

 ment granules have reached the centre of the cpII, has not been 

 determined as yet with certainty. Either 1) the cell processes 

 remain in situ or 2) the more fluid protoplasm follows the mi- 

 grating pigment granules and eventually the entire cell becomes 

 rounded up as in a contracted amoeba. In the latter event it is 

 difficult to imagine how the protoplasmic processes find theii- 

 way back again to the original contour of the expanded cell. 

 Hooker ( ' 12 and '14) has explained away this difficulty by assum- 

 ing, from histological preparations, the existence of Ijanph spaces 

 into which the pseudopodia of the amoeboid melanophore creep 

 or flow. Hooker believes these lymph spaces to be fixed and 

 the melanophore to be a typical amoeboid cell. There are seri- 

 ous objections to this view. 1) Hooker's evidence is adduced 

 fromi fixed preparations and he has been unable to corroborate 

 his observations upon living adult cells ; 2) in the many hundreds 

 of living melanophores that I have observed under high magnifi- 

 cations and the most favorable optical conditions (reflected and 

 transmitted light, dark-field illumination, etc.) I have never been 

 able to detect the secondary migration of the fluid protoplasm, 

 though I have repeatedly watched the same cell in a series of ex- 

 pansions and contractions with this as the sole object; 3) the his- 



