870 



NATURAL HISTORY OF BIRDS. 



gonatous it is sim]>le until bfiiind the end of the shouhler-blades. A glance at onr 

 Figure ITli, as conijiared witli Fig. 173, rej>resenting the dorsal pterylosis of two ano- 

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

 in Sleatonii's, Cuprlmith/iis, Coracias, etc., 



The swifts and the humming birds have neither casca nor a tufted oil gland. This 

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

 natiT, since all the rest, incluiling the Passeres, wore found to have eitiier the one or 

 the other, hence the Cyp.selifonues were set aiimt without further dissent or discus- 

 sion. Tlien Garrod found that all of the species examined by him which had cseca 

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

 feathers were deficient in c»ca. This discovery led to the division of the non-cyj)se- 

 line AnomalogonatfB into two grouj)s, Piciformes with tuft and no ca-ca, 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 



PlO. 172. — PtcryloHis of Hampliailon, 

 dor8ul surface. 



Fig. 173. — Pterjloais of Slenlomit, dorsnl 

 surface. 



Momotida?, ■which are destitute of cajca, were also possessed of a nude oil gland, 

 •while other species had a minute tuft, resort w.-ls had to the theory that the tuft was 

 lost after the two great divisions had l)ranehc(l off, in (mler to e.\])lain this "excep- 

 tion." 



We cannot hel]) thinking that too much stress has been laid upon the conconiitancv 

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

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

 zygodactylous feet with the antio)pelmous plantar arnuigement weighs much more, 

 esjjecially since cuckoos and parrots conclusively ]>rove that these two peculiarities are 

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

 mal avrangfuient as is the syn]i('lnious one should have developed independently in 

 the two groups Piciformes and Passerifornies, while the case of the ^lomotida' proves 

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

 conse<(uenee. 



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

 will need explanation, viz. anisodactylous and pamprodactylous ; the foi-mer indicates 



