370 



NATURAL HISTORY OF BIRDS. 



gonatous it is simple until behind the end of the shoulder-blades. A glance at our 

 Figure 172, as compared with Fig. 173, representing the dorsal pterylosis of two ano- 

 malogonatous birds shows that the bifurcation also occurs among these, as, for instance, 

 in Steatornis, Caprimulgus, Coracias, etc., 



The swifts and the humming birds have neither caeca nor a tufted oil gland. Thi& 

 combination was at first considered unique in the group called by Garrod Anomalogo- 

 natae, since all the rest, including the Passeres, were found to have either the one or 

 the other, hence the Cypseliformes were set apart without further dissent or discus- 

 sion. Then Garrod found that all of the species examined by him which had caeca 

 were lacking a tuft to the oil gland, and that those which possessed this circlet of 

 feathers were deficient in caeca. This discovery led to the division of the non-cypse- 

 line Anomalogonatse into two groups, Piciformes with tuft and no caeca, and Passeri- 

 formes with caeca but no tuft. As the name indicates, the latter, with several other 

 forms, embraced all the Passeres. As it was found out later on that some of the 



FlG. 172. Pterylosis of Ramphastos, 

 dorsal surface. 



FIG. 173. Pterylosis of Steatornis, dorsal 

 surface. 



Momotidffi, which are destitute of caeca, were also possessed of a nude oil gland, 

 while other species had a minute tuft, resort was had to the theory that the tuft was 

 lost after the two great divisions had branched off, in order to explain this " excep- 

 tion." 



We cannot help thinking that too much stress has been laid upon the concomitancy 

 alluded to, and that, by applying it as a divisional character, forms have been artifi- 

 cially separated which are really closely related. With us the concomitancy of the 

 zygodactylous feet with the antiopelinous plantar arrangement weighs much more, 

 especially since cuckoos and parrots conclusively prove that these two peculiarities are 

 entirely independent of each other. It is extremely improbable that such an abnor- 

 mal arrangement as is the synpelmous one should have developed independently in 

 the two groups Piciformes and Passeriformes, while the case of the Momotidae proves 

 that the absence of the feather tuft on the oil gland is a fact of comparatively slight 

 consequence. 



We explained above the two terms, zygodactylous and heterodactylous. TWO more 

 will need explanation, viz. anisodactylous and pamprodactylous ; the former indicates. 



