Abnormal Development of Toad Ova 39 



Central Nervous System — The olfactory lobes extend forward 

 between the nasal fossae. The tissue of the olfactory lobes is 

 somewhat degenerated. The pineal gland consists of a rounded 

 hollow vesicle with a short much dilated stalk. The ventral wall 

 of the third ventricle is abnormally thick. The infundibulum is 

 relatively normal. The walls of the midbrain are also fairly nor- 

 mal but contain some degenerated pigmented cells. The optic 

 lobes are beginning to be differentiated. The hindbrain and 

 spinal cord are relatively normal. 



Organs of Special Sense — The medial walls of the nasal fossae 

 are thick but contain many pigmented and degenerated cells. 

 The eyes are very abnormal. The optic stalks are greatly dis- 

 tended. The pigment layer of the retina is irregular. The sen- 

 sory layer consists of a mass of degenerated cells. The lens is 

 differentiated. The auditory vesicles are simple in form. 



Peripheral Nerves — The sensory ganglia are moderately well 

 developed but the cells are many of them abnormal. Nerve fibers 

 cannot be readily followed. 



Alimentary Canal — The mouth is open. Lips and jaws are 

 clearly marked, although not highly developed. Gill slits are 

 patent, but the gills are not well developed and seem to contain no 

 blood vessels. Opercular folds extend over the anterior portion 

 of the gill region on each side. The oesophagus has a lumen. 

 The tracheo-pulmonary process is short and branched. The 

 stomach lies at the left of the liver anlage. The gut extends 

 straight back. Neither liver nor pancreas is well developed, 

 although masses of cells indicate their anlages. No blood spaces 

 are found in the liver. 



Heart and Blood Vessels — The heart consists of an S-shaped 

 tube, but the walls are not normally differentiated. There is 

 some blood in the ductus arteriosus. There are apparently a few 

 blood vessels present but there is no well developed vascular 

 system 



Genito-Urinary Organs — ^The tubules of the pronephros are 

 slightly dilated. 



Skeleton and Connective Tissues — The chorda dorsalis is rela- 

 tively normal. The cartilages of the head are fairly well developed. 



