194 REYNOLD A. SPAETH 



have presented an opportunity for occasional morphological and 

 embryological observations also. In attempting to categorize 

 any type of cell it is necessary to consider not only its morphology, 

 but its development and physiology as well. An examination 

 of many data of previous investigators, supplemented by my own 

 observations has led me to the conclusion that the melanophores 

 of lower vertebrates do not belong in the category of connec- 

 tive tissue, but are to be considered functionally modified smooth 

 muscle cells. The object of this paper is to summarize the evi- 

 dence for my position. 



MORPHOLOGICAL EVIDENCE 



For our present discussion the following occurrence of involun- 

 tary or smooth muscle in vertebrates is of importance, viz., the 

 digestive tract, the vascular system, the eye and the integument. 

 The units of which smooth muscle tissue is composed consist of 

 elongated or spindle-shaped cells which may be branched or 

 forked, containing a single or several oval or elongate nuclei. 

 In certain cases (sphincter pupillae) the cytoplasm is filled with 

 a dense mass of melanin pigment granules. We may therefore 

 say with Franz ('06), (p. 452) : ''Es ist daher wohl eine zulassige 

 Ausdrucksweise vom Sphincter als von einer Anhaiifung spindle- 

 formiger Pigmentzellen zu sprechen." 



In the lower vertebrates the melanophores occur chiefly in 

 the derma, more rarely in the epidermis (Pouchet 76, in Rhom- 

 bus; Mliller '60, Eberth '67, Pouchet loc. cit., Biedermann '92 

 and many others in the frog; Schmidt '12, in Phelsuma), on the 

 mesenteries and peritoneum and associated with the blood- 

 vessels. Morphologically we find an entire series extending from 

 relatively simple cells with two or three processes to the familiar, 

 extensively branched forms found in the derma. Zimmerman 

 ('93), for example, noted elongated melanophores between the 

 fin rays in several adult teleosts and I have observed similar 

 simple cells in the tail region of adult Fundulus and other teleost 

 species. Franz ('08) has recorded the same condition in the 

 edges of the fins in the larva of Pleuronectes platessa. On the 



