646 FRANCIS M. BALDWIN 



gill region, have changed considerably. The cartilages of the 

 third and fourth arches have now disappeared, except for a small 

 medial portion (basibranchial) , and with this modification, the 

 blood vessels of the corresponding gills have been affected. By a 

 flattening of the ventral surface of the body of the larva, all 

 structures included in the space between the ventral floor of the 

 pharynx, and the ventral wall, present a much crowded appear- 

 ance. As a result of this, the postbranchial body is now forced 

 into a very limited space lateral to the aditus laryngeus muscle 

 and between the ventral wall of the pharynx and the lateral 

 strands of the sternohyoideus muscle of the left side of the peri- 

 cardial wall, where it is reduced to a mass of poorly defined 

 epithelial cells, which, contrary to the usual statements for the 

 other urodeles, contains no conspicuous lumen. This solid mass 

 of epithelial cells is much reduced in length (now about 90 micra 

 long). 



J. The adult postbranchial body. The position and anatomical 

 condition in the adult is somewhat variable. The body is rather 

 inconspicuous and it is practically impossible to recognise it in 

 gross dissection. In transverse sections through the adult head, 

 it is not greatly different from that of the late transforming ani- 

 mal, being a fairly compact oval structure, somewhat irregular 

 in outline, composed of quite large cuboidal cells with a spacious 

 lumen. In position it is somewhat more lateral to the larynx, 

 and the aditus laryngeus muscle, and lies just caudal to the 

 second aortic arch as it turns dorsally to join the dorsal aorta on 

 the left side. I am not able to locate the structure with cer- 

 tainty, in sections of an older head. Whether this be due to the 

 fact that the body has degenerated. and disappeared, or whether 

 it has (as is claimed for it in some forms) become closely associ- 

 ated with the thyreoid (lateral thyreoid) I am not able to say, 

 although I incline to the first of these views, 



4. Carotid gland and epithelial bodies 



Although there is no evidence that the carotid gland in Ambly- 

 stoma arises from cells derived from the entodermal lining of the 



