26 SPOLIA ZEYLANICA. 



greatest tendency to variation. As a consequence, though 

 there are many exceptions, the average Passerine species are 

 confined to smaller areas than less specialized and more widely 

 distributed species and sub-species of other orders. This is 

 well shown by a comparison of the list of birds found within 

 the wide area of the Indian Empire with the list of our smaller 

 area in Ceylon. In the Indian list the Passeres occupy a full 

 half. In the Ceylon list, however, we find that only one-third 

 of our birds or about 120 species are Passerine. It is not so 

 much that Ceylon, taking into account its varieties of climate 

 and configuration, is remarkably poor in birds of the order, 

 but that a very large proportion of the Indian forms are 

 confined to restricted areas, being replaced in other areas 

 within the Empire by different, but closely allied, species and 

 sub-species. 



With such a large assemblage of forms belonging to a single 

 order and possessing the same main structural characters, 

 the task of classification is extraordinarily difficult, and few 

 ornithologists agree in all particulars regarding the grouping 

 of the various species into families, or the sequence in which 

 the families themselves should be arranged. The order is 

 divided primarily into two main groups, based on a difference 

 in the structure of the syrinx, or organ of voice. In the 

 Acromyodi the intrinsic muscles of the syrinx are attached 

 to the ends of the open rings of the bronchial tubes ; in the 

 Mesomyodi these muscles are much simpler, and are attached 

 to the middle of the rings. This division need not, however, 

 greatly trouble the Ceylon student. The Mesomyodi are 

 found mainly in the New World, and only one species of the 

 group, the Indian Pitta — Pitta hrachyura — occurs in Ceylon. 

 It happens to possess a very distinctive plumage, and is also 

 to be diagnosed by the formation of the wing. It has ten 

 primary wing quills,* and the first primary is nearly as long 

 as the second. Many Ceylon Passeres have ten primaries, but 

 in every other such case the first primary is markedly 

 small. 



* The primary qviills are those wliich spring from the pinion — i.e, 

 the outer portion of the wing, bej^ond the " elbow," which is really the 

 joint corresponding to the wrist. 



