42 Charles Russell Bardeen 



filling of the central canal with partially degenerated cells. In one 

 embryo the hind brain and anterior part of the spinal cord are 

 exceedingly rudimentary on one side. 



Of the organs of special sense the eye exhibits the greatest 

 deformities. The nose and ear are as a rule rather rudimentary 

 than markedly deformed. The eye, however, usually shows a 

 patent optic stalk connecting with a space between the pigment 

 and sensory layers of the retina, a lack of differentiation in the 

 sensory layer, and a more or less highly differentiated lens resting 

 against the sensory layer. 



The abnormalities in the alimentary canal are exceedingly variable 

 and may affect any or all parts. The mouth is in all instances 

 patent, the lips and jaws rudimentary. The pharynx and gills 

 vary much in structure in the different embryos. As a rule there 

 are traces of internal gills and of the opercular folds but the gills, 

 owing to lack of development of the vascular system, are rudi- 

 mentary. The oesophagus is patent in some, closed in other of 

 the embryos; the stomach as a rule lies at the left of the anbges 

 of the liver and pancreas. The latter structures are seldom 

 highly developed. The rudiments of the lungs are slightly devel- 

 oped. The intestines may be more or less coiled, but are in none 

 of the embryos highly developed and in some are very rudimen- 

 tary. In many embryos the abdominal cavity is greatly distended 

 while the gut is rudimentary. 



The pronephric tubules are usually greatly swollen in places and 

 this dilatation is also frequently found in the Wolfian ducts. 

 There are seldom distinct traces of the metanephric tubules. 



The myotomes, when not well developed, usually consist of 

 muscle cells somewhat scattered about in the surrounding mesen- 

 chyme. The muscles of the head are usually more or less dif- 

 ferentiated. 



The mesenchyme of the embryos is considerably greater in 

 amount than in normal tadpoles. The cells seem to be spread 

 apart by fluids in the tissues. The cartilages of the head and the 

 chorda dorsalis are relatively normal. 



The ectoderm in most of the tadpoles shows in places outgrowths 

 of an irregular nature. These may be extensive villus-like pro- 



