240 
POPULAR SCIENCE REVIEW. 
and it is conceivable, though there is no fragment of evidence 
in favour of it, that some ancestral aquatic form may have 
developed long fingers and webs like those of the flying frog. 
This speculation does not, however, commend itself to my 
mind as a satisfactory one ; and though doubtless, could we see 
all the extinct forms of life which have existed during the 
secondary period, we should find some creatures developing by 
more or less rapid stages along a definite course in the direction 
of the type of structure selected for our consideration to-day, and 
though I am ready to make an act of scientific faith in the exist- 
ence of such creatures, I confess my imagination fairly baffled 
in its attempts to depict them, or the road which this particular 
course of evolution followed. We must wait patiently for 
more light from palaeontology. But we may wait very hope- 
fully. We may do so because the wonderfully rich harvest of 
fossil remains now being gathered in North America supplies 
us with good and solid ground for hope. 
Already forms have been discovered there so strange that 
they cannot be satisfactorily grouped in any existing order of 
mammals — forms such as imagination could hardly have anti- 
cipated. We may, then, not unreasonably expect that sooner or 
later — perhaps very soon — fossils deeply buried in the secondary 
rocks will come to light, clearly pointing out the line which 
has been followed in the evolution and development of the 
only truly flying mammal — the bat. 
EXPLANATION OF PLATE CXXXYI. 
Fig. 1. A Flying Fox from Samoa, Pteropus Whitmeei. 
Fig. 2. Skeleton of a Flying Fox. 
Fig. 3. Side yiew of breast-bone of ditto. 
