THE GRASS WARBLERS OF SOUTH AFRICA. 
(Cisticola and Hemipteryx .) 
By Austin Roberts. 
The diagnostic characters of Cisticola so clearly mark it off from other 
African genera of the Sylviidae that it is hardly necessary for me to dwell 
on them here ; but the characters distinguishing Hemipteryx from Cisticola 
are not so well known, and it is the aim of this discussion to define clearly 
the differences between these two genera ; in doing so I have found it 
convenient to deal with all the species at present known to occur in South 
Africa, to show why the two genera should be regarded as distinct. 
Cisticola , as being the best known and comprising the greatest number 
of species, will be treated first, 
Cisticola , Kaup.* 
Before dealing with the species individually, it is necessary for me 
to make a few general remarks on the relationship of the genus to others 
in the Sylviidae , in order to advance a few simple reasons in favour of 
keeping this genus intact. In this connection, two questions of evolution 
lequire consideration, namely “ divergence ” and “ convergence.” By 
the former is meant, in the present instance, that while a number of genera 
may now display a certain amount of divergence of habits from those 
which were once common to them all, they still retain somewhat similar 
kabits in general ; and, in proportion to their divergence from their once 
common habits, show 7 a common relationship in their appearance struc- 
turally. By “ convergence ” is meant that, though some genera now 
show a great similarity of habits and appearance with those of other genera, 
we are still able by investigation to trace back, to a limited extent, their 
origin, which we find is different from that of the other genera. The 
internal anatomy of members of this family shows so little difference of 
uny account inter se that little notice of it has been taken in classification ; 
the external structure only, such as the shape of the feathers, limbs, and 
hody, need therefore be considered in this discussion. The term “ habits ” 
Tnav be here defined as the nature of a bird’s environment, its manner of 
Alight, and many little points which strike the naturalist as peculiar to 
certain birds in a wild state. Nest-building habits and egg- characters are 
useful guides, not only because they can be studied in collections, but 
also because they may be closely compared with the birds themselves 
in many cases; and wre had better consider them apart from the more 
.generalized term “ habits.” Some notable examples of divergence and 
convergence are to be found in the Sylviidae, and by applying the principles 
* Naturl. Syst., 1829, p. 119. 
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