210 REYNOLD A. SPAETH 



tological preparations of Ballowitz ('93) show nerve termina- 

 tions on the processes of the melanophores which could not have 

 any physiological significance if the entire cell were withdrawn 

 from these processes; 4) finally I have repeatedly corroborated 

 in Fundulus, the observation of Ballowitz ('13) concerning the 

 position of the nucleus following a proximal migration of the 

 pigment granules. Not infrequently in an expanded melano- 

 phore, the nucleus may be seen to lie far out from the centre in 

 one of the processes. If such a cell be contracted, all the pig- 

 ment granules accumulate at the centre, but the nucleus remain 

 in its original position in the process. Under favorable condi- 

 tions it may actually be seen in the contracted cell, lying in the 

 process, with a considerable area of pigment-free cytoplasm be- 

 tween it and the central mass of melanin granules. In any case, 

 upon reexpansion, the nucleus is found practically to have re- 

 tained its original position. It is difficult to correlate these 

 facts with Hooker's conception. 



At present it is, then, impossible to say that the melanophores 

 are certainly not amoeboid cells in the mature condition, though 

 the weight of the evidence appears to be against such a view. 



The question now arises as to what a proximal and distal mi- 

 gration of pigment granules w^ithin a stellate cell can have in 

 common with a 'contraction' in smooth muscle. A physical- 

 chemical analysis of the melanophore may serve to clarify the 

 comparison. 



Considered as a physical-chemical system the melanophore 

 consists essentially of a colloidal suspension of melanin granules 

 (the disperse phase) in a dispersion medium which is itself an 

 exceedingly fluid sort of protoplasm i.e., an emulsoid sol. 'Con- 

 traction' of the melanophore consists of an aggregation of the 

 disperse phase of melanin granules and in 'expansion' there is 

 an increased dispersion of the melanin granules. In other words, 

 when the melanophores are stimulated to contract, we observe 

 the first step in a reversible aggregation or coagulation process, 

 i.e., the aggregation of the melanin granules. Is it possible to 

 consider this phenomenon a reversible coagulation such as occurs 

 commonly in emulsoids? The size of the melanin granules is 

 relatively so large (ca. 0.0004 mm.) that we should rather expect 



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