491 
hibits a well marked optic vesicle while the nerve system shows 
clearly the three primary brain vesicles and the beginning development 
of hemicerebra. The stomodeum is marked and two branchial arches 
are present, the first arch has already divided into maxillary and 
mandibular portions. The study of the left embryo is more difficult, 
as it does not present a profile view. i 
3. The monster represents about seventy two hours incubation. 
It exhibits a double caudal extremity, each of which is composed of 
nine somites. The remainder 
of the body seems normal. 
4. This chick (Fig. 3) was 
obtained through the courtesy 
of a former student. It hatched, 
but is about one third below 
normal in size. How long it 
lived was not ascertained. It 
exhibits a single head, one pair 
of wings and four legs. Upon 
gross examination it is double 
from apparently the Jower sacral 
region, caudally, At this region 
of bifurcation an area of tri- 
angular form (about 6 mm. each 
way) is noted. The tissues 
here are soft and the area quite 
deep. Upon dissection (Fig. 4) 
this area was found to be an 
opening into vertebral canal 
(spina bifida) the soft tissues 
previously mentioned repre- 
senting nerve tissues covered Fig. 4. Dissection showing high bifur- 
by the neural sheaths and thin cation of the vertebral column and exposure ot 
: ‘ ee : the vertebral canal. The triangular area was 
skin. This condition involved covered by the skins and spinal meninges. 
the lower cervical and upper 
thoracic vertebrae. Caudad to this opening the body is double. On the 
left portion five thoracic segments can be counted below the point of 
bifurcation, while on the right the divisions are not well marked. It 
will be noted that the right canal is open for a greater extent than 
the leit (Fig. 4). The monster is double from the lower cervical 
region, a condition not apparent in the gross specimen before dissection. 

