650 THE POPULAR SCIENCE MONTHLY. 



noting, however, that the manus is already a little the wider and more 

 prominent. 



In Fig. 7 the manus is not only larger but has protruded so as to 

 display the wrist and elbow regions, and a slight prominence upon the 

 anterior border marks the position of the thumb (pollex). In these 

 three specimens I have not as yet found the ear, but in 3 and 4 the 

 eye is quite apparent. 



In Fig. 6 the ear is a triangular flap, as in most early mammalian 

 embryos,^ 



The manus and pes have enlarged and present shaded portions 

 corresponding with the thinner tissue between the finger and toes. 

 In the former this is to become the web ; in the latter it is wholly re- 

 moved so as to leave the toes free. The muzzle is partly covered by 

 the manus, but it is already somewhat pointed, as in the next figure. 



In Fig. 9 the manus and pes of the left side are shown as if re- 

 moved from the trunk, so as to expose the flat and prominent muzzle. 

 The ear is a large flap, but still projects forward so as to cover the 

 opening. The pollex has separated from the other digits, and the 

 latter are elongated and bent downward. The pes is longer and the 

 signs of subdivision more distinct. A web connected the limbs and 

 the trunk as in the older specimens, but it was somewhat torn, so that 

 the exact extent could not be determined, and I preferred to wait for 

 a better specimen to show it. 



The specimens above described were taken from a Brazilian species, 

 I^yctino7nus Brasiliensis (which is also found in this country). Figs. 

 10 and 11 were from the common " little brown bat " ( VespertUio subu- 

 latus). As might be expected, the increasing limbs are packed about 

 the body more or less irregularly. But in Fig. 10 the limbs of the two 

 sides are placed with almost exact symmetry so as to cover the face 

 and the body. One eye is covered, the other peeps out over the index- 

 finger. The ears are firmly held down by the thumbs, and one of the 

 nostrils is partly hidden by the web. The lower part of the trunk 

 and the tail are bent upward, and the knees are thrown outward so as 

 to bring the great-toe (jor) upon the outer instead of the inner side. 

 The whole suggests an efibrt upon the part of the embryo to not only 

 occupy the least possible space, but also to screen itself from obser- 

 vation, and neither see, nor hear, nor smell. 



In Fig. 11 is shown an older embryo, of natui-al size, outspread so 

 as to display the characteristic features of bats ; the greatly-elongated 

 fingers ; the separation of the thumb ; and the extension of the web, 

 with the reticulated arrangement of vessels and neiwes upon it. This 

 nervous expansion seems to enable bats to perceive the proximity of 

 bodies by the change in the pressure of the air. 



^ It remains to be seen whether the seals, whales, manatee, and dugong, have a pinna 

 in the earlier stages, and afterward lose it. Upon the earliest embryo of a manatee yet 

 known, see a paper by the writer in American Journal of Science, August, 1875. 



