220 THE ZOOLOGIST. 
In man the greater part of the alimentary canal is composed of 
a tube of small diameter—the small intestine—which is continued 
onwards as a more capacious one, the large intestine. These two 
are not simple continuations one of the other, but the former 
enters the latter obliquely, the nearer end of the large intestine 
remaining free as the “blind gut” or cecum. In the Swallow and 
Sparrow, as in all the Passeres, instead of there being a single 
ccecum at the place of junction of the two intestines, there are two. 
These are not found in the Swifts, nor in the Humming Birds. 
In the Swallow, the Sparrow, and all their true allies, it is 
always the case that the tendons which contract up the last joints 
of the toes are so arranged that the birds have the power of 
folding the toe which corresponds to our great toe (the one 
directed backwards) without moving any of the others. In the 
Swift, however, whenever the great toe (the hallux) is fully flexed, 
it is impossible that the other toes should remain opened out, 
because the two muscles which act on one and the other are 
bound together by a tendonous band. 
In the Swallow, the Sparrow, and most singing birds the number 
of feathers in the tail is twelve. In the Swifts and Humming Birds 
the number is always ten—another important difference. 
In the Swallow also, as in all the passerine birds, there is a 
slender muscle running through the thin triangular membrane of 
the wing between the arm and the fore arm, which is quite 
peculiar in the manner of insertion or attachment, no other birds 
possessing the same arrangement. In the Swift this muscle 
terminates in quite a different manner, here again resembling the 
Humming Birds exactly. 
Taking these several characters into consideration, and realizing 
how little they are susceptible, on account of their deep-seatedness, 
to the influence of slight external changes in the mode of life of 
the species, we are inevitably driven to the conclusion that their 
weight is overwhelmingly greater than that of the superficial simi- 
larity which is so readily brought about by the similarity of the 
circumstances under which the two species are accustomed to live, 
and that the resemblances between them are, so far as their con- 
stitutions are concerned, dependent only on the fact that they both 
have—with different pedigrees—arrived at a superficial similarity 
in contour because they subsist exclusively on the same food. 
