1886. | GEOCOCCYX CALIFORNIANUS. 469 
The spinal pterylosis is represented by two broad, longitudinal 
tracts well separated from each other in the middle line by a naked- 
skin area overlying the vertebral column. These spinal pteryle 
gradually converge towards each other as they approach the pelvic 
region, over which they merge into one feather-space, which becomes 
pointed behind and terminates just in front of the nude oil- 
gland. 
The upperside of the coccygeal protuberance is also sparsely 
feathered, being divided from a more generously covered area below 
by the line of horizontally arranged pits for the quill-butts of the 
rectrices of the tail. An exceedingly narrow tract, on either side, 
springs from the posterior margin of the outer bifurcation of the 
ventral tract just below the arm-pit, to run longitudinally down the 
side, in front of the thigh, to become lost before it arrives at the 
margin of the vent. This strip seems to be composed simply of a 
double row of feathers, and might appropriately be termed the 
lateral tract. 
The patagium of the arm is very thinly feathered anteriorly, 
while its dorsal aspect is quite completely covered ; the remainder of 
the pterylosis of the pectoral limb presents us with nothing of a 
peculiar nature. The posterior marginal- boundary of this “ alar 
tract”’ is, as usual, terminated by the row of quill-butts of the 
primary feathers of the wing. 
Passing now to the crural region, we find a posterior limb but 
sparsely feathered, while a conspicuous ‘‘ femoral tract’ extends 
obliquely across the dorsal aspect of the thigh, and rapidly narrow- 
ing, runs along the pubic line, finally merging into the “ caudal 
tract.’ 
Geococcyx shows its best-marked apteria in front, in the mesial 
space between the inner strips of the ventral tracts, and laterally to 
the outer side of the spinal pterylosis, where, indeed, for a con- 
siderable space no feathers may be said to occur at all. A well- 
marked dorso-longitudinal naked area is also to be seen. In this 
Ground-Cuckoo we notice a membrane, stretching between the 
thigh and leg, which corresponds to the patagial fold of the pectoral 
limb, and fully as well-developed. 
Before closing this part of our subject it is of interest to observe 
the general form of Geococcyx, which, now that its feathers have 
been removed, can be studied to the best advantage. It will be seen 
how perfectly its figure has come to assume a shape best adapted to 
the peculiar requirements of the bird. Its pelvic limbs are large, 
muscular, and consequently powerful, while the pectoral ones are 
decidedly less so, though by no means weak or inefficient. The 
body-form of this prince of avian racers is what almost might be 
called “clipper built,” so admirably fashioned is it to the needs and 
ends of a rapid running bird of the size of our subject. 
With these few remarks upon the external organization and 
appearance of Geococcye we will now close this part of our discussion, 
and pass to the consideration of some of the features presented in 
the structure of the remainder of its economy. 
