Observations on the development of the excretory system in Turtles. ß39 



would alone account for a considerable amount of the growth in length 

 but I doubt whether it will account for all of it. 



To show the number of funnels not finally closed off from the 

 coelom in these stages we may tabulate the conditions found in 

 several embryos: 



III (4) Som. 5 G 7 8 9 10 



Funnels R 2 3 3 2 Total 10 



„ L 4 2 2 „ 8 



IV (1) Som. 5 6 7 8 9 10 

 E, 1 2 2 3 2k ^ Total 10 or 11 



L 12 3 3 2/^ „ 11 or 12 



V (2) Som. 5 6 7 8 9 10 



R 13 4 3 2 Total 13 



L 13 2 1 „ 7 



VI (2) Som. 5 G 7 8 9 10 



R 13 3 5 2 Total 14 



L 13 2 4 2 „ 12 



From what has been said above it is obvious that beyond the sixth 

 somite which seems to be the anterior limit of the mesonephros, one 

 cannot say how many of these tubules are pronephric. On account 

 of their segmental origin we should expect that there would be only 

 six pronephric tubules, but as the fusion with the mesonephric ele- 

 ments comes in before the tubules are fully formed, it is impossible 

 to say whether the increase in number is due to this factor alone or not. 



In stages III— VI, Plates 46 and 47, there are in some cases several 

 funnels (1 — 3) before there is any sign of a continuous duct. On the 

 other hand, in some cases we find the duct continuous from the first 

 tubule which appears. This may be on either side, as indicated by 

 the irregular appearance of the basis, or, more rarely, the first tubules 

 may be nearly opposite. The so-called "collecting duct" is therefore 

 very imperfect, here, as a rule. In the pronephric region, the duct 

 is evidently formed by the fusion of the tip of each tubule with the 

 tubule following. Further back, the duct seems to develop by the 

 division of its own cells or through genetic relation with the ecto- 

 derm as indicated above. As early as stage III the duct reaches and 

 opens into the cloaca. 



In the majority of embryos older than II, as noted before the 

 pronephric tubules and the mesonephric tubules in the same region 

 open into the coelom by a single funnel. This opening generally 

 becomes more and more median and more contracted until at the en<^ 



45* 



