Abnormal Development of Toad Ova 27 



differentiated. The chorda dorsalis is fairly regular in form except 

 at the anterior end, where some of the cells seem completely to 

 have disappeared, and in the region of the medulla, where it is 

 asymmetrical in places. 



Musculature — A number of the muscles of the head are fairly 

 well developed. The individual muscle cells are in some instances 

 highly differentiated. The myotomes are fairly normal except 

 next the undeveloped region of the spinal cord on the left 

 side. 



Skin — In several places there are villus-like outgrowths of 

 epithelium. 



Larva No. 2, Experiments II, Plate III 



External Form — The caudal extremity of the embryo bends 

 sharply in a dorsal direction. The body cavity is enormously 

 distended, although the alimentary canal is but slightly developed 

 (see sections c to /). In these sections the ventral wall of the body 

 cavity has collapsed, owing to the action of the fixing fluids. The 

 head is exceedingly irregular in shape, owing to the imperfect 

 development of the organs of special sense and the abnormal 

 accumulation of a loose mesenchyme. The mouth opens on the back 

 of the head anterior to the anterior nares. Apparently there is no 

 sucker. Along the dorsal margin of the posterior end of the body 

 and the tail, folds of tissue project (sections h and t). 



Central Nervous System — The ventral end of the central ner- 

 vous system consists of a thin-walled dilated sac which does not 

 extend as far forward as the nasal fossae. Sections a, band c show 

 no trace of it. Sections d, e and / show the abnormal condition 

 of the walls of the neural tube. There is no fibrilar framework 

 (Randschleier). The cells are irregularly placed; many of them 

 show evidences of degeneration and not a few lie free in the neural 

 canal. The pineal gland is a small vesicular pouch, the walls of 

 which are composed of cells which exhibit degeneration. The 

 infundibulum consists of a thin-walled projection from the ven- 

 tral portion of the neural canal. Section d shows the entrance 

 into it. The spinal cord consists of a round thin-walled tube in 

 which no specific differentiation has taken place. 



