Abnormal Development of Toad Ova 37 



Musculature — Mere traces of muscles are found in the region 

 of the head. The more anterior myotomes consist of rounded 

 masses of cells on each side of the chorda but not in contact with 

 this (section e). In the center of the trunk and in the tail they are 

 somewhat more normal in form. 



Skin — Projections of epithelium may be seen on the dorsal 

 margin of the tail (section g) and at the side of the ventral wall of 

 the body cavity (section e). There are curious subcutaneous 

 vesicles on each side of the head posterior to the sucker. Section b 

 shows one of these at the left of the section. 



Larva No. 7, Experiment II, Plate IV — B 



External Form — The tail is short and stubby and curves dorsally. 

 The heart is shrunken and irregular in outline. The sucker is 

 apparently fairly normal. 



Central Nervous System — Two well separated olfactory lobes 

 project forward as far as the nasal fossae and each is in contact 

 with the medial wall of the corresponding nasal fossa (section a). 

 The tissues of the olfactory lobes are partially degenerated. The 

 lateral ventricles are very small. The lateral walls of the third 

 ventricle are thick and partially differentiated (section b). The 

 pineal gland projects above the third ventricle and its tissue is 

 partly degenerated. The infundibulum is small and thin-walled. 

 The lateral walls of the mid-brain are thick and project inward 

 so as to nearly obliterate the aqueduct. The hind-brain is rela- 

 tively normal, although flattened from front to back (sections c 

 and d). The spinal cord in places is fairly normal, in places the 

 cells from the walls of the neural tube fill or nearly fill the central 

 canal. 



Organs of Special Sense — ^The nasal organs are fairly well dif- 

 ferentiated. They lie, relative to the brain, posterior to the nor- 

 mal position. The pigment layer of the retina is separated by a 

 space from the sensory layer. The latter is not well diflferentiated. 

 The optic stalk is not patent but contains no nerve fibers. A lens 

 is present. The auditory vesicles are simple in form. 



Peripheral Nerves — Cranial and spinal ganglia are moderately 

 well developed. The nerve fibers cannot be readily traced. 



