36 Charles Russell Bardeen 



a group of little differentiated ectoderm cells. The auditory 

 vesicles are simple in form, thick-walled, and resemble those newly- 

 formed in the embryo. 



Peripheral Nerves — Mere traces of the sensory ganglia of the 

 cranial and spinal nerves can be seen. Nerve fibers are not well 

 marked. 



Alimentary Canal — The mouth is a large opening into the 

 pharynx. The opening is irregular in outline and its boundary 

 presents mere traces of a beak and lips. The pharynx is dilated 

 anteriorly (section a), but over the cardiac region is flat and bent 

 to conform to the dilated pericardial cavity. The gill clefts 

 nowhere open to the exterior but instead are laterally stopped up by 

 massesof epithelial tissue (sections). No gills are specifically differ- 

 entiated. The oesophagus is filled with epithelial cells. Thetracheo- 

 pulmonary process is rudimentary. The oesophagus passes directly 

 back into a primitive intestine. Neither liver nor pancreas seem 

 specifically differentiated, although the anlages of each are repre- 

 sented by masses of yolk" cells (section ^). The gut consists of a 

 mass of cells which extends in a fairly straight direction from the 

 oesophagus to the anus. Anteriorly it shows some tendency to 

 form convolutions, and in the mid-body region it curves slightly 

 toward the right side of the body. For the greater part of its 

 course no lumen is present. 



Heart and Blood Vessels — The pericardial cavity is very thick- 

 walled anteriorly but is relatively large. More distally the ven- 

 tral wall is thin (section c). Traces of a heart can be seen (sec- 

 tions c and d). This forms a slightly S-shaped structure with 

 thin-walled ductus arteriosus and sinus venosus (section d) and a 

 more solid ventricle (section c). There is no blood in the heart 

 cavity. No definite blood vessels can be made out in the embryo. 



Genito-Urinary Organs — The tubules of the pronephros are 

 much dilated. The Wolfian ducts can be traced only part of the 

 way to the anlage of the cloaca. In the distal part of their course 

 they are curious flat tubes (section /, on each side of body). 



Skeleton and Connective Tissues — The chorda dorsalis is slightly 

 asymmetrical in places. The connective tissue is excessive, espe- 

 cially in the head. The cartilages of the head are not distinct. 



