1891.] The Genesis of the Chromatophores in Fishes. 117 
; Š 
I was enabled, through the courtesy of Dr. C. O. Whitman, to 
examine the records of previous observations during my stay at 
the Marine Biological Laboratory at Woods Holl. Although I 
then found that many of my observations were but verifications 
of those of others, it has seemed best to publish my account 
because I have examined new material, have worked out the 
matter in greater detail in several species, and do not agree with 
the previous observers in all points. 
Aubert? Kupffer’ Agassiz and Whitman,‘ Wenkebach,’ and 
List ê all seem to agree in deriving the chromatophores from the 
mesoblast; as to when and where they arise these authors 
naturally vary with the different species examined. 
All the figures, excepting 37, were made from living eggs or 
larvæ, with a Zeiss microscope and Abbe camera. The letters 
A and D refer to the objectives, the 2 and 4 to the oculars, ot 
Ziess. 
EXPLANATION OF PLATES. 
PLATE I,.—Sciena saturna, Figs. 1-6, a portion of the embryonic ring, 
showing the chromatophores. In Fig. 1 they are all still contained in the 
embryonic ring. In Fig. 2 a few are seen entering the segmentation cavity. 
Figs. 3 and 4 show a portion only of the region covered by Figs. I and 2, 
with more cells in the segmentation cavity, Fig. 4 being drawn five minutes 
later than Fig.2. Figs. 5 and 7 show still later stages, in which a still larger 
number of cells have been freed; Zeiss, D and 4. Fig. 7, an optical section 
of the segmentation cavity (s. c.), near the embryonic ring, showing the 
large chromatophores, the thin ectoderm lying above them, and the parablast ` 
below them. Fig. 74, the same at some distance from the embryonic ring, 
the chromatophores being much less numerous. Fig. 8, a series of eight 
free chromatophores of Aypsopsetta guttulata; D and 4. Fig. 9, the same 
cells 134 minutes later. Fig. 10, a series of five chromatophores. Fig. 
2? Beiträge zur Entwickelungsgeschichte der Fische. Zeitschr. f. wissensch. Zool., VIIL, 
1856, 
8 Beobachtungen über die Entwickelung der Knochenfische. 
IV., 1868. 
* The Pelagic Stages of Young Fishes. Mem. Mus. Comp. Zool., pp. 7and 40, 1885. 
5 Beiträge zur Entwickelungsgeschichte der Knochenfische. Arch. f. mikr. Anat., 
XXVIII., 1886, 
ê Zur elgg Ns der Knochenfischen (Labriden). Zeitschr. f. wissensch. Zool., 
XVL., x 
Arch f. mikr. Anat., 
