PARENTAT. CARE AMONG ERESH-WATER FISHES. 499 



Oil exaiiiiniiii;- the male at the breediiij? season, the kidneys are seen to I>e 

 considerably swollen, the enlargement lieing especially noticeal)le i)osteriorly 

 (fig. 1 A). Sections of the kidneys reveal an altered condition of the simious 

 tubules (fig. 1 A. /)), the conical epithelial cells of Avhich are swollen at their 

 free ends and indefinite in outline. The nucleus of each cell is slightly dis- 

 placed and occupies a more terminal position than in the normal condition. 

 These epithelial cells are active in secreting the material used in constructing 

 the nest. They perform the function, indeed, of cell glands, and their secretion 

 is carried l>y the uriniferous tul>es to the <uter ventral border of each kidney, 

 where a large duct passes longitudinally. In cross section the ureters (pi. 

 I. fig. 1 A. a. a) are oval, and their cai)acity is very great at this time, the 

 walls being of dense fibrous tissue lined with pavement epithelium. Both 

 ureters emerge from the renal mass near the posterior end, and descending in 

 a forward direction become applied to the wall of the so-called urinary l)lad(ler, 

 which at this point is somew^hat attenuated, and passing anterioi-ly they open 

 obli(piely from without inward into the bladder. This structure, it is unneces- 

 sary to say, is not morphologically coiniected with the urinary receptacle of 

 higher vertebrates, the lengthened course of the ureters, of which it is simply 

 a dilated common jiortion, being due to its extraordinary development in the 

 male stickleback. In a fish 5^ inches in length it is alwut an inch long, and at 

 its widest part one-fifth inch in diameter. Situated on the right side of the 

 abdominal cavity, innnediately below the swim bladder in the jiosthepatic 

 region, it has the form of a capacious p.vriform sac, ending blindly anteriorly, 

 and diminishing in circumference as it passes backward (pi. i, fig. f, a). 

 Before terminating posteriorly it describes a double curve, crossing over the 

 intestine from the right to the left side (pi. i, fig. 6, ?>), and after a short 

 liarallel course passing on the ventral side of the intestine to the right side 

 again (pi. i, fig. 6. c), debouching behind the genital pore (pi. i, fig. (">. fl) 

 into a urinogenital sinus, forming the posterior poi'tion of a cloacal depression 

 Oil. T. fig. 0, (?), into which also the anus opens (pi. i, fig. G, f). The wall 

 of the bladder consists of two layers, an internal epithelium (pi. i, fig. 1 B, «), 

 which is readily detached, and a dense external connective layer (pi. i. fig. 

 1 B, />), which thins out as the blader enlarges anteriorly. Traces of an inter- 

 mediate muscular layer appear posteriorly where the walls are extraordinarily 

 thickened. The descending ureters (pi. i, fig. 1 B, c c) approach opposite 

 sides of the bladder, that on the left proceeding obliquely below the common 

 duct of the vasa deferentia, and passing forward and merging in the walls of 

 the bladder on the left side. 



This union is shown in the same transverse section which shows the luiion of 

 the vas deferens of the left testis with that of the right. The course of the right 

 ureter is shorter and more direct, as the bladder lies on that side of the aiidom- 

 inal cavity at this point. It coalesces with the right w^all of the bladder pre- 

 ( isely opposite the left ureter. As the bladder descends to cross the intestine 

 inferiorly it twists, so that the left ureter is brought to the central side of the 

 cervix of the bladder. Both return to the lateral position as the bladder crosses 

 the intestine. The intestine now curves to the right, and the relations of the 

 ureters become reversed, the right being below and the left rising to the dorsal 

 side of the bladder. They increase rapidl.y in capacity, showing in cross section 

 an extremely elliptical cavity, and as the bladder enlarges they pass obli(iu<»ly 

 into its chamber, their walls being continuous with the external la.ver of the 

 bladder. Along this tortuous course the viscid secretion of the renal tul)ules 

 reaches the bhulder, where it is stored up. When first formed the secretion is 

 simply a plastic jelly ; but a fibrillar structure appears to rapidly develop in it. 



