480 



The Embryology of Hylodes Martinicensis 



of yolk-cells, usually solid * at every point except near the middle yolk- 

 mass. The rod, little by little, from behind forwards, is separated from 

 the central mass of yolk, and covered ventrally by the splanchnic meso- 

 derm (Fig. E, F, g). A continuation of the mesentery which slings the 

 yolk-mass in the middle region supports the anterior portions of the rod or 

 gut (Figs. B3, El, m) ; but no mesentery is present dorsal to the cloaca. 



The posterior gut at stage VII 

 has been separated from the yolk 

 and completely surrounded by 

 the mesentery as far forward as 

 the level of the anterior limit of 

 the hind legs. The gut up to 

 this time lies in the median line. 

 After stage VII, additions to the 

 gut are still made from the dor- 

 sal part of the yolk-mass, but on 

 the left of the median line (cf. 

 Fig. C, hg). As the process 

 goes on, the gut necessarily en- 

 croaches upon the middle region. 

 The first steps in the development of the anterior end of the digestive 



be 



Fig. D. Cross sections of stage IV, to show 

 the formation of the posterior gut; 1 anterior 

 to 2 (and posterior to AS), ac, archenteric cav- 

 ity; be, body cavity; g, gut; y, yolk-mass. 



Fig. E. Cross sections of stage VI, to show the connection between the posterior gut and 

 the yolk. 1 to 4 from before backwards (posterior to Fig. B3). be, body cavity ; cl, cloaca ; 

 da, dorsal aorta; g, gut; m. mesentery; ma, mesenterial artery; pvc, posterior vena cava; 

 "Wd, VI olfiian duct; y, yolk-mass. 



tract are not apparent in my series. In stage II the anterior portion of 



' I have seen sections of the tadpole of Rana, in which the archenteron at 

 an early stage is closed for a short distance. 



