Abnormal Development of Toad Ova 3 1 



several coils forward and finally passes back into the rectum. 

 This is greatly dilated and partly coiled. The anus is small and 

 apparently partly stopped up by mucus. The ventral wall of 

 the body cavity is strikingly thick, not only in front of the heart but 

 also over the entire abdomen to the anus. 



Heart and Blood Vessels — The heart is thin-walled but fairly 

 well formed. There are some trabeculae in the ventricle. The 

 pericardial cavity is small, owing to the great amount of mesen- 

 chyme in the body wall. Some, at least, of the chief blood vessels 

 are present and contain a considerable amount of blood. 



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

 irregular in form and are much dilated in places. The Wolfian 

 ducts may be followed to the cloaca. Near the cloaca the anlages 

 of the tubules of the mesonephros may be seen. 



Skeleton and Connective Tissue — The chorda is relatively nor- 

 mal. An excessive amount of mesenchyme is present, especially 

 in the region of the head. In the head most of the cartilages are 

 fairly well developed. 



Musculature — In the head the muscles are fairly well differen- 

 tiated. The myotomes are fairly normal although the cells are 

 somewhat more scattered than usual. 



Skin — In places irregular finger-like processes of the epithelium 

 project from the body. 



Larva No. 4, Experiment II, Plate IV — A 



External Form — ^The tail is a mere rudiment. The ventral part 

 of the body is much swollen, owing to distention of the body cavity. 

 The head is small and deformed. The sucker is rather flat (sec- 

 tion a). 



Central Nervous System — The neural tube ends anteriorly in 

 two thick walled olfactory lobes. The right one is shown on the 

 left side of section a. The cells in the walls are irregularly placed 

 and many exhibit signs of degeneration. The Randschleier is not 

 normally disposed. There is a small pineal body with a narrow 

 lumen and thick walls composed of cells not specifically differen- 

 tiated. The optic lobes are partially differentiated. The infun- 

 dibulum has a thin wall but contains in its cavity a large mass 



