45*; 



THE AMERICAN NATURALIST 



[Vol. XLV 



pigmented leucocytes since they have no similarity to the 

 latter, nor are pigmented leucocytes found in negro 

 blood. In the cutis he claims to be able to see all the 

 transition stages between pigment-free connective tissue 

 cells and such as are strongly pigmented. On the basis 

 of his findings he thinks it appears only reasonable that 

 in the pigmenting skin (transplanted white) the earlier 

 unpigmented granules (Reinke's trophoplasts ; Alt- 

 mann's bioblasts) of the chromatophore take on a dark 

 color (by as yet unknown ways) and that this is connected 

 with the presence of blood ; and that it can not, however, 

 be regarded as the product of fragmentated red cor- 

 puscles. Melanin may be hemosiderin, but is the product 

 of a living cell. His final position thus approaches some- 

 what to Meirowsky's, though they still differ as to the 

 cell that elaborates the pigment for the epidermis. It is 

 important in this connection to note that while Karg de- 

 scribes numerous branching pigmented connective tissue 

 cells (wandering cells) among the epidermal cells of the 

 transplanted white skin, he failed to find such in the nor- 

 mal skin of the negro. He thinks it probable that such 

 may be found in the skin of the negro embryo. 



Meirowsky in his monograph also gives a very com- 

 plete review of the literature to date. He uses experi- 

 mental methods mainly. His findings supporting the first 

 view may be briefly summarized: Pigmentation is pos- 

 sible in the epidermis without the agency of "melano- 

 blasts," or even any aid from the cutis. There are both 

 epidermal and cutis melanoblasts, and they are inde- 

 pendent of each other. Pigmented epidermal cells are 

 capable, under certain stimuli, to assume irregularly 

 branching forms (filling the intercellular spaces) simu- 

 lating mesodermal chromatophores (so-called melano- 

 blasts) which might have wandered into the epidermis. 

 This is probably the correct interpretation of Karg's 

 figures. He brings forth cytological evidence to show 

 that the pigment arises from a reddish nuclear sub- 

 stance (a 1 1 pyroniuroter Kernsubstanz")— he does not 

 commit himself as to its chemical nature— which passes 

 into the cytoplasm and gradually assumes the yellowish 



