726 DEVELOPMENT OP THE COMMON PHALANGER, 



In an embryo of 36 mm., greatest length, or from head to 

 rump, 33-5 mm., hair is found over most of the body, with the 

 e.x;ception of the following regions, which are hairy later, and 

 which are .still l:)ald, — a median strip from the forehead to 

 between the shoulders, sides of the mouth, ears, backs of the 

 hands, margins of the pouch, hind legs except on outer surfaces 

 of knees where hair is just appearing, tail and perineal region. 

 The vibrisspe are now seen, but none of the other large hairs. 

 Though hairs are thus present over the greater part of the surface, 

 the embryo not only at this stage, but for long after, on super- 

 ficial examination looks quite naked. This is owing to the hairs 

 being very fine and short, and also ver}^ few in number. When 

 the surface is examined by the low power of the microscope the 

 minute hairs are seen to be regularly arranged, and each from 

 one-half to one-third of millimetre distant from its neighbour. 

 The principal measurements at this stage are: — Head, 14 mm.; 

 snout to tail, 57 mm.; tail, 12 mm.; arm, 13 mm.; leg, 9*5 mm.; 

 foot, 5 mm. 



In embryos larger than the preceding, the greatest length gives 

 but a \ery imperfect idea of the size, as owing to the length and 

 flexibility of the body the embryos are found variously curved. 

 The embryo shown in figure 12 measures in a direct line from 

 head to rump, iO mm , or to the curve of the tail, 43 mm. As 

 showing the irregularity in development, the vibrissas in this 

 embryo are not yet through the surface, although the embryo is 

 very distinctly larger than the preceding. The body hairs are 

 very similarly developed; the bald patch on the back of the head 

 is smaller in size. Thex'e is still no hair on the backs of the 

 hands, on the feet, tail, or ears. The claws on the hind toes are 

 very well marked, and the little claw or nail on the hallux quite 

 distinct. The pinna of the ear is now quite free and folded 

 forwards. The line of the united eyelids can be distinctl}^ made 

 out. The following are the principal measurements : — Head, 15 

 mm.; snout to tail, 62 mm.; tail, 15 mm.; arm, 15 mm.; leg, 12 mm.; 

 foot, 6 mm. The rapid proportional growth of the hind quarters 



