Abnormal Development of Toad Ova 33 



the right side of the body between the rudimentary tail and the 

 body cavity (section /). The body cavity is greatly distended 

 (sections d^ e, f). 



Heart and Blood Vessels — The heart is a simple S-shaped tube. 

 The ductus arteriosus is patent; the ventricle has very thick walls, 

 a small lumen and no trabeculae. The sinus venosus and the 

 auricle are thin-walled. There are a few blood corpuscles in 

 the lumen of the heart. Mere traces of blood vessels are visible. 



Genito-Urinary Organs — The tubules of the pronephros are 

 much dilated. They lie in large spaces which here and there con- 

 tain a few blood corpuscles (section d). The Wolfian ducts are 

 much distended (section e). 



Skeleton and Connective Tissues — -The chorda is relatively nor- 

 mal in structure. There is an excessive amount of connective 

 tissue, especially in the region of the head. The cartilages of the 

 head are partly differentiated. There are no auditory capsules. 



Musculature — The muscles of the head are partially differen- 

 tiated. The myotomes are relatively fairly well developed (sec- 

 tions d and e). 



Larva No. 5, Experiment II 



External Form — The tail curves dorsalward. The abdomen 

 is distended. The head is somewhat irregular in form. The 

 sucker consists of a short projection on the right side of the body. 



Central Nervous System — Anteriorly there are two small olfac- 

 tory lobes. The lateral ventricles extend but a short distance into 

 each. The pineal body is round and has a slender stalk. The cells 

 composing the body are more or less scattered, although the 

 outer wall of the body is fairly smooth. The lateral walls of the 

 third ventricle are thick and show a fairly normal differentiation 

 into cells and Randschleier. The hypophysis has a very thin wall. 

 The optic lobes are not differentiated. The fourth ventricle is 

 much distended. The walls of the medulla contain many degen- 

 erated pigment cells. 



Organs of Special Sense — The tissue of the medial wall of each 

 nasal fossa contains many degenerated pigment cells. The pig- 

 ment layer of the retina is separated from the sensory layer. 



