628 
Mr. G. L. Bates on the 
(2) Gap in the Spinal Tract in certain Sylviidae. 
In certain genera forming a very natural group, largely 
African, of which Cisticola may be taken as typical, there is 
a marked gap in the spinal tract immediately behind the 
saddle, and the lower end of the saddle itself is often 
emarginate or cordate in outline. This gap is sometimes 
entirely without feathers of any kind, but usually bears a 
few small semiplumes in a more or less regular row, but no 
contour-feathers. It extends from the saddle halfway to 
the oil-gland. The specimen of Calamocichla rufescens 
figured had a few semiplumes on this part. Specimens of 
Camaroptera griseoviridis had not even the semiplumes, 
but had a perfectly bare gap from the saddle for 5 mm. in 
the direction of the tail. The same was true in the one 
specimen examined of Bathmedonia rufa and in one of 
Macrosphenus concolor. In a half-fledged specimen of 
Prinia mystacea there was a perfectly bare gap extending 
for 10 mm.—a long way in so small a bird ; but in adults 
of the same species the corresponding portion bore a few 
small semiplumes. 
Besides the species already mentioned, the following were 
examined—generally more than one specimen of each—and 
found to have this gap:— Cisticola erythrops , Burnesia 
hairdi, B . leucopogon , Apalis binotata , Macrosphenus flavicans , 
Camaroptera superCiliaris , Sylviella virens , S. denti , and 
Eremomela badiceps . 
Some other species of small birds somewhat similar to 
the above, and generally placed near to them, were found to 
be without such a gap in the spinal feather-tract. Among 
these may be mentioned Phylloscopus trochilus , Stiphrornis 
a: ant hog aster, and Hylia prasina ; in these the spinal tract, 
though narrow behind the saddle, was continuous, bearing 
contour-feathers all the way. 
The gap here described is doubtless a degeneration of the 
portion of the spinal tract most clearly overlapped by the 
long and abundant plumage of the saddle. But in birds of 
other groups examined in which the feathers of the saddle 
