IV 



COELOME 



201 



In the Am- 

 phibia and Amni- 

 ota the pericardiac 

 cavity becomes 

 telescoped back A. 

 into the general 

 peritoneal cavity, 

 its hinder wall be- 

 coming extended 

 so as to form a 

 thin membranous 

 bag enclosing the 

 heart and separat- 

 ing it from the 

 other viscera. 



Apart from the 

 walling off of the 

 pericardiac from 

 the main periton- 

 eal cavity there is 

 found in the case 

 of the Amniota a 

 well-marked tend- 

 ency for the latter 

 cavity to undergo 

 further subdivi- 

 sion, special por- 

 tions becoming 

 more or less com- 

 pletely walled in 

 by secondary fu- 

 sions taking place 

 between apposed 

 portions of the 

 peritoneal lining. 



Fig. 110. — Differentia- 

 tion of the myotome 

 as seen in transverse 

 sections of Lepidosiren 

 larvae. 



A, stage 30 ; B, stage 31 + ; 

 C, stage 32 ; D, stage 35 - ; 

 E, dividing myoblasts of 

 inner "wall from stage 36. 

 m&', 'myoblasts of inner 

 "wall ; mb", myoblasts of 

 outer wall ; m/, contractile 

 fibrils ; vac, vacuole. The 

 contractile fibrils cut across 

 are shown as distinct black 

 dots. 



c. 



iiif * * i& ^ 





E. 



