Lilian Y. Sampson 



485 



tained where the second and third rudiments originate. Ko trace re- 

 mains of the place of evagination of the first rudiment from the gut itself. 



Mouth. — The stomodsum is from its first appearance (after stage IV) 

 slit-shaped, and lies well under the ventral surface of the head (cf. Fig. 

 15, Plate II). A free passage from the stomodseum into the mouth 

 cavity is not established until stage X. 



A noteworthy fact in the development of the mouth is the entire ab- 

 sence of horny jaws, and teeth, and of fringed lips. The hardened tip of 

 the upper lip which develops late in embryonic life will be described in 

 another place : it has not the characteristics of a tadpole tooth. It may 

 be here noted that an adhesive gland is also wanting. The tongue is 

 first found in stage YII. 



Visceral Pouches. — The visceral pouches first appear in the series in 

 stage III. It has been noted that, in surface view, there are four ecto- 

 dermic depressions. In section, it is found that the hyo-mandibular pouch 

 is a deep diverticulum from the wall of the 

 pharynx and that its entodermic lining in many 

 cases lies in contact with the outside ectoderm ; 

 the first branchial pouch is in almost the same 

 condition, but not in actual contact with the 

 ectoderm; tlie second branchial pouch is merely 

 a shallow diverticulum, and the third barely be- 

 gun. In stage IV (Fig. J), the same conditions 

 exist, except that the third branchial pouch has 

 become deeper. After stage IV the pouches 

 are gradually redi'iced, and before VIII have 

 almost disappeared. 



Not one of these pouches in any preparation 

 can be demonstrated to open to the outside, 

 hence the evidence as far as it goes shows that 

 no true gill-slits are formed in the embryo of 

 Hylodes. Before this conclusion can be placed 

 entirely beyond doubt, it is necessary that a more 

 complete series of embryos be examined. 



The statements of earlier writers in regard to the gills have been 

 entirely confirmed. Not a trace of either external or internal gills can 

 be found in any of the embryos. It will be shown later that the circula- 

 tion in the gill arches is extremely simple. 



(Esophagus and Lungs. — The lungs are derived from a single rudiment 

 which arises in stage V by a constriction of the ventral portion of the 

 oesophagus from the dorsal (Fig. K). As the rudiment becomes more 



Fig. J. Horizontal section 

 through the branchial 

 pouches in stage IV. br 1, 

 br 3, br 3. 1st, 2d. 3d branchial 

 poucli ; lim, hyomandibular 

 pouch. 



Fig. K. Cross section of 

 the oesophagus and rudi- 

 ment of the lung in stage V. 

 oe, oesophagus ; rlu, rudi- 

 ment of lung. 



