MELANOPHORE A TYPE OF SMOOTH MUSCLE CELL 197 



Sphiiicterfasern und mesodermalen Chromatophoren aufstel- 

 len;" and again: ''Denn es scheint in mehr als einer Beziehung, 

 dass die Chromatophoren nichts anderes als verkappte Muskel- 

 zellen sind." 



Many of the older investigations upon the responses of the 

 melanophores to various stimuli were carried out upon living 

 animals. Here the situation was exceedingly complex since so 

 many physiological factors had to be controlled. In a previous 

 paper ('13 b) I have called attention to this objection and have 

 described a method whereby the melanophores of teleosts, es- 

 pecially Fundulus heteroclitus, may be removed from the fish 

 and stimulated in a variety of ways without the slightest me- 

 chanical injury in manipulation. The technique is exceedingly 

 simple, consisting of the careful removal of the scales with their 

 superficial sheets of dermal melanophores. These scales are 

 readily transferred from one solution to another and, by selecting 

 adjacent scales from the same fish, we obtain very satisfactory 

 physiological units whereby it is possible to test the effects of a 

 series of solutions — the degree of expansion or contraction of 

 the pigment serving as an indicator of relative stimulation. In 

 preparations of this sort in which the circulation and nervous 

 control have obviously been eliminated, I have found that chemi- 

 cal stimuli such as 0.1 N KCl, heat (30^ C), ultra-violet light and 

 induction currents all bring about a more or less rapid contrac- 

 tion of the pigment granules. Furthermore, in indifferent media 

 like Ringer's solution or olive oil, the melanophores remain ex- 

 panded for long periods. It therefore seems justifiable to con- 

 sider the contracted phase that of stimulation, since the melano- 

 phores respond by contracting to the above familiar series of 

 physiological stimuli. Throughout the following discusssion I 

 shall consider the contracted phase of the melanophores as cor- 

 responding, physiologically, to the contraction in smooth muscle. 

 The objections to the application of the term 'contraction' in 

 the case of the melanophores, I shall take up at the close of this 

 section. 



