24 Charles Russell Bardeen 



liver. The liver and gall bladder are highly differentiated. The 

 posterior end of the liver and the bile duct are shown between the 

 CEsophagus and stomach in section /. The gall bladder lies dor- 

 sal to the liver somewhat anterior to the level of this section. The 

 entrance of the bile and pancreatic ducts into the gut takes place 

 considerably posterior to this level. The anus in this embryo 

 passes out between the anlages of the posterior limbs (section g). 



Heart and Blood Vessels — The heart is much larger than that 

 in the control embryo previously described. The ventricle is 

 crossed by large trabeculae (section e). The auricle is beginning 

 to be divided into right and left halves. The blood vessels are 

 dilated with blood. The vessels seem to correspond with those 

 described for the 12 mm. tadpole by Marshall (Embryology, Fig. 

 76, p. 166). 



Genito-Urinary Organs — The tubules of the head kidney are 

 greatly coiled. The tubules of the mesonephros are differentiated 

 near the cloaca. More anteriorly the anlages of these tubules 

 consist of dense masses of cells. The genital folds are not promi- 

 nent. 



Skeleton — The differentiation of the vertebrae has scarcely 

 begun in this embryo. The chief cartilages of the skull have 

 appeared (see Marshall, Embryology, p. 262, Figs. 90, 91 and 

 92). A moderate amount of mesenchyme surrounds the differ- 

 ent organs. 



Muscles— The chief muscles of the head are clearly differen- 

 tiated. In the trunk the myotomes are larger than at the preced- 

 ing stage and the muscle cells are more highly developed. 



The abnormalities exhibited by the experiment larvae may be 

 illustrated by a few typical examples. 



Larvae No. i. Experiment II, Plate II 



External Form — This embryo exhibits a marked dorsal flexion 

 of the body near the middle of the trunk, so that the long axis of 

 the tail is at right angles to that of the anterior portion of the 

 trunk and the head. The bend seems due largely to an abnormal 

 dilatation of the hind-gut. The head is quite irregular in shape, 

 the deformity of outline being due to great abnormality in the 



