788 PROFESSOR W. C. M'INTOSH 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 (PI. XXV. fig. 3). The 

 simple epithelial walls of the excretory ducts (sg) 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 especialty 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 Wolffian 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 PI. 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 (PI. XXV. fig. 5). These folds are continuous with the two excretory 

 ducts, which, as formerly stated, open into the upper 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 (ne). 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 (PI. 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 VII. figs. 1, 3, 4, 6), such 

 a cutaneous sub-layer being found in Amphioxus 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 



