524 A. B. DAWSON 
 D. Effects of adrenalin 
Lieben (’06) found that, in the frog, injections of adrenalin 
into any of the veins, body cavity, or lymph spaces caused a 
contraction of the melanophores. Necturus shows a similar 
response to adrenalin. An intracoelomic injection (concentration, 
1 in 200,000) produced a complete contraction: of the melano- 
phores in about three and a half hours. This condition persisted — 
for almost twenty-four hours. 
E. Mechanism of contraction 
1. In other Amphibia. The mechanics of the movements of 
pigment cells is still a disputed question. Many workers claim 
that the chromatophores are actively moving amoeboid cells. 
Others believe they are fixed stellate cells within which the pig- 
ment moves. Recent observers are agreed, however, that the 
proximal and distal migrations of pigment occur along fixed 
paths. Among the early workers the constancy of form of the 
pigment cells was not appreciated. The majority of them 
regarded the chromatophores as amoeboid cells contracting and 
expanding in intercellular spaces without following any preformed 
definite paths. Hooker (’12, ’14 b) and Holmes (’138, 714) believe 
that the melanophores are amoeboid and that contraction and 
expansion are brought about by pseudopodia, but, according to 
Hooker (14 b), the cells have constant expansion-phase patterns, 
which are forced upon them by the preformed spaces in which 
they lie. 
Biedermann (’92) took an intermediate position, and claimed 
that, while the processes shortened in contraction, they were 
never completely withdrawn. Winkler (10 b) induced con- 
traction and expansion of melanophores by electrical stimulation, 
and found that in general the pigment follows old paths, but in 
some instances it may extend into positions not previously noted. 
In contraction, he believed, the pigment-free processes shortened, 
but he was unable to follow the movement very far. According 
to Kahn und Lieben (’07), in contraction and expansion the 
pigment moves in preformed paths and the form of the cell is 
