648 THE POPULAR SCIENCE MONTHLY. 



With the more advanced embryos the promiuent ear would be con- 

 clusive against their avian nature, and the nostrils, where they show, 

 are not those of birds. 



We may, then, dismiss from our minds any anxiety as to whether 

 bats are partly birds and partly mammals, and conclude merely that, 

 upon the essential mammalian structure, there have been superinduced 

 features which enable the bat to fly in the air ; these, however, no 

 more making it a bird than the form and habit of the whale and mana- 

 tee render them fishes. 



The second question is, whether bats are to be regarded as the pro- 

 genitors or the descendants of the moles and shrews ; or, to put it 

 more accurately (since the idea of derivation does not imply that living 

 species have descended from other living species, but from similar 

 extinct species or from others which combined features since separated 

 in the two forms), is it probable that the existing bats have been pro- 

 duced from original stocks more nearly resembling the moles or the 

 reverse ? That the former is the more probable, is indicated upon three 

 grounds : 



1. The bat form is peculiar among mammals, and does not, like the 

 Ornithorhynchus and Echidna^ manifest any internal structural afiinity 

 with birds. There is a much more marked resemblance to the extinct 

 flying reptiles {Pterodactyli), but this is probably one of analogy. 



2. The embryo bat resembles the ordinary small mammal ; the long 

 fingers, the persistence of the web between them, and its continuation 

 from the border of the body and tail, are features of later appearance. 



3. In one embryo (Fig. 9), the thinness and prolongation of the 

 muzzle as compared with the lower jaw may be compared with the 

 elongated snouts of the " star-nosed mole " and the " elephant shrew." 



I have never had the opportunity of examining the young of moles 

 or shrews. This would be very desirable, and, one would think, not 

 difiicult to accomplish. 



Figs. 5 to 11 are intended chiefly to show the gradual develop- 

 ment of the limbs, so the other parts are drawn with less detail, and 

 no attempt is made to elucidate the manner of formation of the face 

 from the visceral arches. 



The series begins with Fig. 5. Here the body is simply an elon- 

 gated mass, longer and rounded at the head end, and tapering at the 

 other extremity. It is twisted upon itself, as is often the case with 

 young embryos. The yolk-sack and membranes are not well preserved, 

 and are not shown at all in the figure. This embryo may be regarded 

 as quite small for even a bat. The limbs have not appeared, so the 

 tail does not form a distinct prolongation. (The lower figure is of 

 natural size ; the upper is enlarged five diameters.) 



In Fig. 6 the arm {ar) and leg {pes) project as little flat pads 

 from the sides of the body. There is no sign of subdivision into fingers 

 and toes, and very little difierence between the two limbs. It is worth 



