196 EEYNOLD A. SPAETH 



chyme cells. From the region of Kupffer's vesicle there develops 

 a fan-shaped area of migrating cells which rapidly spread out on 

 the surface of the yolk. These cells eventually give rise to con- 

 nective tissue, the yolk melanophores, the endothelial cells and 

 possibly also to the smooth muscle cells in the walls of the larger 

 blood vessels. For some time after the pigment has begun to 

 develop within the wandering cells that are destined to become 

 melanophores, they continue to show active amoeboid move- 

 ments. In a transparent pelagic egg like that of the scup (Steno- 

 tomus crysops), these w^andering cells at the posterior end of 

 the embryo may be observed with startling clearness. 



It is impossible to draw any sharp morphological or embryo- 

 logical distinction between certain pigmented connective tissue 

 cells and chromatophores (Leydig loc. cit.) just as there are mor- 

 phological transitions between connective tissue and smooth 

 muscle cells (Flemming '97). We can say, then, that typical 

 connective tissue cells, melanophores and smooth muscle cells are 

 all known to develop from mesenchyme and furthermore, that 

 smooth muscle cells (sphincter pupillae) and possibly also melano- 

 phores (Borcea loc. cit.) may develop from the ectoderm. The 

 embryological evidence is thus at least not negative." 



PHYSIOLOGICAL EVIDENCE 



By far the most striking evidence of the parallelism between 

 smooth muscle and melanophores is furnished by physiological 

 experiments. Franz ('06) first recorded the striking similarity 

 between the physiological responses of the sphincter pupillae in 

 Acanthias and the dermal chromatophores of the frog. He noted 

 1) that both respond to light by contraction, 2) that indifferent 

 gases like N and H elicit no contractions of the chromatophores 

 and that these gases prevent the contraction of the sphincter 

 pupillae upon illumination; 3) that after death, the pigment 

 cells and sphincter are both contracted. He then says (p. 453) : 

 "Wir konnen also in mancher Hinsicht Analogien zwischen den 



- It is certainly not without interest in this connection that the chromato- 

 phores of cephalopods have been found to develop from single smooth muscle 

 cells by a complicated metamorphosis (Chun '02) . 



