Lilian Y. Sam23Son 487 



hatching, have attained no great size and are remarkably simple in 

 structure. In sections of the late stages, and in adults preserved in alco- 

 hol, they appear as hollow thin-walled sacs, not showing the trabecular 

 structure of the lung of the common frog. In all sections of late embry- 

 onic stages, the walls of the lungs are more or less wrinkled, so that 

 in life they may have been capable of expansion to some extent; in their 

 present condition, however, they extend, at most, only slightly beyond the 

 anterior limit of the liver. 



Differentiation of the alimentary canal, after stage VIII, is accompan- 

 ied by the disappearance of yolk from its walls, and by the absorption of 

 the large yolk-mass that still separates the anterior part of the intestine 

 from the posterior (cf. Figs. Bl, and for the size of the yolk relative 

 to the embryo) . The yolk first disappears from the walls of the pharynx. 

 In closed portions of the gut, the lumen as a rule reappears immediately 

 upon absorption of the yolk, but the roof and floor of the broad low 

 oesophagus remain pressed together, even after there is no yolk remaining 

 in them, and the opening to the lungs is not re-established until after stage 

 XII. The stomodaeum is open into the entodermal buccal cavity at stage 

 X (as already stated), so that after XII, there is free communication 

 from the lungs to the outside. Posterior to the lungs, the walls of the 

 oesophagus, after the reduction of the yolk in their cells (stage XII), 

 become convoluted but no lumen exists until after hatching. The convo- 

 lutions may be partly due to shrinkage in the preparations, although in 

 an older specimen where food has entered the stomach, the walls remain 

 distended after preservation ; this seems to indicate that the walls remain 

 collapsed until food has passed through the gut. The stomach portion 

 of the gut retains its lumen from the time of its formation. The intes- 

 tinal portion continues to be lengthened after stage VII by additions 

 from the yolk, has a small lumen, and becomes convoluted about stage 

 XII. The walls of the posterior gut lose their yolk first in the cloact, 

 then in the portion near the yolk, and lastly between these parts. As in 

 the anterior gut, the walls become convoluted in stage XII. The lumen 

 near the middle yolk is enlarged in stage XII and extends through the 

 gut for some distance posterior to the yolk. 



Since the posterior gut is constantly added to from one side (the left) 

 of the yolk, and the anterior from the other side, it comes about that the 

 two connections between gut and yolk pass each other, and a middle 

 region between them does not exist after stage XII in the same sense as 

 before. Still there remains a large amount of yolk, which after stage XI 

 does not retain its solid condition (see Fig. M), and is no longer reduced 

 by gradual contributions to the more differentiated parts of the <rvit 



