20 J. A. BADERTSCHER 
right ultimobranchial body in the same pig is represented by a 
single area which extends through a series of ten sections. Judg- 
ing from the so variable developmental behavior of these 
structures in pig embryos, this single area (and similar single 
areas in the thyroid gland of other pigs) undoubtedly does not 
represent the greatest length of the central core of this ultimo- 
branchial body, but only what is left of it at the time the pig 
was killed. It underwent a more rapid transformation than the 
left one. 
A considerable lapse of time intervenes between the age of the 
pigs and the young adult hogs, thus producing an undesirable 
break in the continuity of the postnatal developmental history 
of the ultimobranchial bodies. Although the conclusion in re- 
gard to these structures in the young adult hogs is thus rendered 
somewhat uncertain, I have a strong feeling that the areas of 
small follicles in the thyroid of the young adult hogs nos. 1 and 2 
represent the ultimobranchial bodies in an advanced stage of 
development. Their structure, location in the thyroid gland, 
and their proximity to unusually large follicles strengthen this 
- interpretation. 
In some of the later developmental stages of pig embryos it 
was found that unusually large (cystoid) follicles develop in 
connect’on with the ultimobranchial bodies. The extent and 
location of areas of this type of follicles in the thyroid gland of 
postnatal pigs need therefore to be considered. 
The existence of a possible interrelationship between the large 
follicles and the ultimobranchial bodies is exemplified in a single 
thyroid gland in scme of the postnatal pigs. Thus, in the pig 
at birth the ultimobranchial body that is present is located in 
the middle third of the left lateral half of the thyroid gland, 
while an area of large follicles occupies an almost corresponding 
position in the right lateral half of the gland. Also a few very 
large follicles are found near the most caudally located segment 
of the ultimobranchial body. In the thyroid gland in pig 7.5 
days old large follicles are found in the immediate neighborhood 
of the right ultimobranchial body and near the central segment 
of the left one. Also cephalad to the most anteriorly located 
