996 



DEVELOPMENT OF THE URINARY AND SEXUAL ORGANS. 



convolution formed independently penetrates, and here it becomes closely 

 surrounded. The duct of the kidney later empties separately into the urogenital 

 sinus, and becomes the ureter. The point where the branching begins becomes 

 the site of the pelvis of the kidney; the branches themselves become the urinary 

 tubules. Toldt found as early as the second month complete Malpighian bodies 

 in the human kidney; in the fourth month Henle's loops. The urinary blad- 

 der arises in its first indication as early as the fourth week, becoming more 

 distinct in the second month from the first portion of the allantois (Fig. 392, 

 4, a). The upper portion passes over into the middle ligament of the bladder 

 as the obliterated urachus, which often remains permeable for a short distance 

 beyond the bladder; although even in adults there often persist, in the lower 

 third of the urachus, unobliterated portions, which may give rise to cyst-forma- 

 tion. 



According to Keibel, the development of the bladder takes place in such a 

 manner that the common cloacal space is divided by two lateral folds into an 



anterior (the rudimentary 

 urinary bladder) and a poste- 



V rior space (rectum). Con- 



genital communications be- 

 tween the bladder and the 

 rectum are thus easily ex- 

 plained as developmental de- 

 fects. Congenital fissure of 

 the abdominal wall and the 

 bladder results from persistent 

 patulousness of the blastopore. 

 Internal Organs of Gener- 

 ation. In front, and internally 

 to, the Wolffian bodies there 

 develops in the mesoblast the 

 longitudinal, projecting sexual 

 gland (Fig. 392, I, D), which 

 originally is the same in both 

 sexes (hermaphroditic stage) . 

 In addition , there forms parallel 

 to the Wolffian duct (W) a 

 canal, which empties down- 

 ward likewise into the urogen- 

 ital sinus, the duct of Miiller 

 or the sexual duct (M). The 

 sexual gland appears first as a 

 longitudinal protuberance, and 

 is covered with the high epi- 

 thelium of the mesoblast, the 

 germinal epithelium of Wal- 

 deyer. The duct of Miiller 

 (which is not yet present at 

 the fourth week) appears at 

 first as a linear furrow in the 

 germinal epithelium, which 

 then becomes deeper and con- 

 stricts itself off to a cord that 

 is at first solid, but later be- 

 comes hollow. The upper out- 

 let of the duct opens free into 

 I n +^~ ~,^.'^-.:- :;'" -- o ^ both ducts fuse for a sbiort dis- 



E 



r 



FIG. 



39I- Transverse Section through the Primitive Kidney the 

 Rudimentary Duct of Miiller, and the Sexual Gland in a Chick 

 at the Fourth Day (after Waldeyer); enlarged 160 times: m, 

 mesentery, L, abdominal wall; a', the region of the germinal 

 epithelium from which the anterior extremity of the duct of 

 Muller (z) has invaginated itself; a. thickened layer of the 

 germinal epithelium, in which the primary germ-cells (G and 

 lie; h, mesenchyma, from which the stroma of the sexual 

 gland is formed; WK, primitive kidney; y, duct of the primi- 



the oviduct (//, 



. -_ ^-^^^i^ij.j.xuj.^0 vjj. uuuii, me uterus (/) 



^ male sex the germinal epithelium is lower (although at first it still 



^SB^ttgESME***** 



