788 PROFESSOR W. C. M‘SINTOSH AND MR E. E. PRINCE ON 
month after hatching, mesoblastic cells become aggregated along the whole dorsal extent 
of the two ducts, especially in the fore and hind regions, and they present a somewhat 
glandular character, minute sinuous tubules appearing in their midst, which pass down 
and open into the longitudinal ducts. Plate XXVI. fig. 3, shows this elongated renal 
mass of segmental tubules, and presents largely the features of the permanent renal bodies. 
Still better is the relation of the parts seen in the section (Pl. XXV. fig. 3). The 
simple epithelial walls of the excretory ducts (sq) are fibrous and thickened, and become 
in fact the permanent ureters. GEGENBAUR views the pronephros as the primitive excre- 
tory gland of the Chordata, whose place has been taken by the mesonephros, and we see 
that while the pronephric ducts persist the phylogenetic replacement of the pronephros by 
the Wolffian body is ontogenetically repeated. It is noteworthy that the segmental ducts 
become much convoluted along their course, but especially in the fore-portion. What- 
ever this may signify, these primitive archinephric ducts are the same as those which in 
Elasmobranchs and others connect the serial segmental tubes, but in Teleosteans they do 
not appear to divide longitudinally into upper or Wolftian ducts and ventral generative 
canals. The connective tissue which surrounds the renal organs becomes deeply 
pigmented at a very early stage (PI. VII. figs. 1, 3, 4, and 7), the large black corpuscles 
continuing to increase until their structure in later embryonic stages becomes obscured 
on account of the profuse distribution of these bodies (vide Pl. XVII. figs. 1 and 2, and PI. 
XXVI. figs. 3 and 4). The close connection of the early segmental ducts and the rudi- 
ments of the pectoral fin has been pointed out, and it is interesting to note that the 
black pigment, surrounding the renal organs at a later period, extends over and is con- 
tinuous with the pigment-layer which passes to the base of the developed fin. The wall 
of the urinary bladder at a subsequent stage presents a consistent connective-tissue layer 
(conn), lined with columnar epithelium (epith), which in the upper portion forms pro- 
minent folds (Pl. XXYV. fig. 5). These folds are continuous with the two excretory 
ducts, which, as formerly stated, open into the wpper and anterior wall of the vesicle. 
The Integument and Embryonic Pigment.—Throughout embryonic life the in- 
tegument remains thin and transparent, so that the internal structure of the young fish 
is readily seen. No cilia can be detected upon it. As already pointed out, a flattened 
external layer or stratum corneum (ep, Pl. IV. figs. 5a—5d) is distinguished from the 
subjacent layer, the neurodermis (ve). Soon after the notochord is defined these two 
layers extend as a distinct integument, not only over the dorsum and flattened parietes 
of the embryo, but as a yolk-sac, over the vitelline globe (Pl. VII. fig. 6). The 
neurodermis, later in embryonic life, consists of several layers of pulpy rounded 
cells, which gradually merge into the flattened epidermis above. The innermost part of 
the two-layered epidermis constitutes a stratum Malpighii, and from it apparently exudes 
a lymphatic plasma, which forms a distinct fluid layer (ss, Pl. VIL figs. 1, 3, 4, 6), such 
a cutaneous sub-layer being found in Amphiowus and the Cyclostomes, though separated 
from the epidermal layers by the dermis proper. In Teleosteans when the mesoblast 
extends beneath the epidermis, to form the cutis proper, such a separation will be also 
