BODY 

 SEGMENTS 



100 HOURS 

 STAGE 26 



5 DAYS 

 STAGE 28 



7|8 |9 |10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31|32|33|34|35|36|37|38|39|40| 



Mullerian duct 



pronephros 



metonephric blastema 

 cloaca 



mesonephros ." I ' ^^"^^^^^s^EJ^sr" 



tail gut 

 proctodeum 



pronephros 



nephric duct 

 ureter 



cloaca 



B 



mesonephros „j,^ i 



^ adrenal 



gonad 



6 DAYS 

 STAGE 31 



dorsal aorta 



8 DAYS 

 STAGE 34 



BODY 

 SEGMENTS 



dorsal aorta 



/" ' ii i i M(j i M)^i i i i n iii i i ii iTmi 



caudal artery 



metanephros. 

 Mullerian duct 



pronephros adrenal 



gonad mesonephros 



urodeum 



7 I 8|9|l0|ll|l2|l3fl4ll5|l6|l7|l8|l9|20|2l|22|23|24|25|26|27|28|29|30|3l|32|33|34|35|36|37|38|39|40| 

 CERVICAL I THORACIC | LUMBAR | SACRAL I CAUDAL 



Figure 10-10. Developmental stages of the urogenital system of the chick in terms of somite posi- 

 tion and age. (After Witschi, 1 956) 



bules are little more than cords of cells extending from a 

 slight funnel to a small vesicle. At first the vesicle of 

 one segment does not attach to that of the next. From about 

 the fourth or fifth vesicle back they join as the nephric duct 

 which lies just below the posterior cardinal vein. The pro- 

 nephros has about 10 tubules at this stage and extends pos- 

 teriorly to about the 15th somite. The most posterior tubules 

 are S-shaped like those of the mesonephros. 



At the posterior end of what appears to be the pro- 

 nephros (funnels indicated for each tubule), the posterior 

 cardinal is inconspicuous and the nephric duct moves out- 

 ward and upward to lie above the mesonephric blastema. 

 Here the nephric duct expands and knots of nephrogenic 

 cells appear ventromedial to it, just behind the level of the 

 vitelline artery. Some tubules are developed and enter the 

 nephric duct. The nephric duct extends back to the last 

 conspicuous (27th to 28th) somite. Glomeruli are not apparent 

 at this stage, although at the anterior end of the pronephros 



a few swellings into the body cavity, adjacent to the aorta, 

 are observed. 



In the 72-hour chick the pronephric elements are still 

 present; two or three asymmetric funnel remnants and vesi- 

 cles lie to either side, above the coelomic cavity in the region 

 of the lung buds. The nephric duct begins a few somites back 

 from the first vesicle. Funnel remnants are apparent at in- 

 tervals. At the posterior end of the pronephric region, two 

 or three complete S-shaped tubules are present with open 

 funnels. Behind these, several tubules have detached (sepa- 

 rate) funnels. Distinct glomeruli are lacking but bulges for 

 them lie medial to the peritoneal funnels. 



In the 96-hour chick small glomeruli project into the 

 cavity above the lung buds (somites 9 to 10), but the pro- 

 nephric rudiments are inconspicuous. The pronephros now 

 consists of bits of tubules lying in the 6th to about the 15th 

 somites, and some vestigial glomeruli in the 12th to 16th 

 somites. The nephric duct lies below the anterior cardinal 



298 



THE UROGENITAL SYSTEM 



