136 The Microscope, 



row of tooth-like structures, or a combination of these with cilia, 

 which surround the mouth of the capsule. This, in many 

 species, is an object of great beauty under the microscope, and 

 in the variety of its structure forms one of the most useful char- 

 acteristics in the systematic study of the mosses. 



THE MICROSCOPIC STRUCTURE OF CERTAIN 

 FEATHERS. 



DR P, L. HATCH, 



PRESIDENT MINNESOTA ACADEMY OF NATURAL SCIENCE. 



II. 



WE see here the manner in which the continuous web of a 

 feather is formed which, within the range of a certain 

 measure of force, will enable the vane to resist strain ; the 

 anterior series of barbules with its armature crossing and 

 overlapping the posterior down through which the booklets are 

 thrust, the cilia remaining on top to antagonize them and main- 

 tain their adjustment. The diagonal direction which the two 

 series of barbules sustain to each other allows the hooks of a 

 single one of the upper series to successively grasp a correspond- 

 ing number of the barbicels of the lower, thus forming a delicate 

 network of meshes, the partitions of which are hard, polished, 

 and rounded above, allowing the air to pass freely through the 

 entire wing in its upward movement, but which in its downward 

 stroke, by the pressure of the air upon the convex surface of the 

 curved inferior expansion of the shaft of the barb, closes the 

 meshes of each feather of the entire wing completely. When 

 this arrangement is fully understood there is no longer any 

 .mystery about the question of how a bird flies. The elastic, 

 membraneous, lower portion of each barb in these wing feathers, 

 as well as in those of the tail of all aerial birds, is so adapted 

 to the webbed, inter-barb space between the parallel shaftlets of 

 the barbs constituting the same, that no air can possibly pass 

 through upward while the bird is on the wing, while by the 

 same arrangement the upward motion of the wing meets with 

 little resistance. The larger portion of the feathers investing a 

 bird are called, in taxonomic parlance, contour feathers. 



Possessing all of the essential elements before stated, some of 

 them are greatly modified in the details of their structure, a few 



