Abnormal Development of Toad Ova 29 



section / it may be seen between the gut and the tracheo-pulmon- 

 ary process. 



Heart and Blood Vessels — The heart apparently consists of a 

 thin-walled tube which has been ruptured. The only blood vessels 

 which can be made out in the embryo are irregular sinuses contain- 

 ing a small number of blood corpuscles. 



Ge}7ito-Urinary Organs — The pronephric tubules are rudimen- 

 tary and are irregularly drawn out in the distended wall of the body 

 cavity (section /, on the right side of the section). The Wolfian 

 ducts cannot be followed uninterruptedly to the cloaca. They lie 

 far out in the body wall on each side. In places they are dilated, 

 in places apparently missing. 



Skeleton and Connective Tissues — The anterior end of the 

 chorda is small and defective (section /). In the spinal region it 

 is relatively normal (sections h and z). There is an excessive 

 amount of loose mesenchyme throughout the body, especially in 

 the region of the head. A few of the cartilages of the head are 

 developed, though apparently not perfectly normal in form. 



Musculature — In the head a few groups of partly differentiated 

 muscle cells indicate muscles. The outlines of the trunk myo- 

 tomes are not distinct. The muscle cells are. more scattered than 

 normal, owing apparently to their being forced apart by the invasion 

 of fluids and mesenchyme. 



Skin — There are numerous places in which the epithelium 

 gives rise to finger-like projections. The most marked of these is 

 the dorsal margin of the trunk and the tail. 



Larva No. 3, Experiment II 



External Form — The posterior half of the body, including the 

 tail, bends sharply in a dorsal direction. This is due to a great 

 dilation of the hind gut. The head is rounded and swollen and 

 it is difficult to make out clearly the specific characters of the tad- 

 pole head. The sucker is rather flat. 



Central Nervous System — The central nervous system ends 

 anteriorly in two distinctly separated olfactory lobes into which 

 the lateral ventricles extend but a short distance. The walls 2 re 

 abnormally diff^erentiated and contain both cells and fibrous tissue. 



