1909. | OF THE THIRD TANGANYIKA EXPEDITION, vt 
species of the genus Schizopera have been found in the Central 
African lakes, seven of them occurring in Lake Tanganyika. On 
a closer examination, it has been proved that none of these 
species is identical with the type-species, S. longicauda, ex- 
hibiting as they do some well-marked differences of apparently 
specific value. Of course, it would be quite unreasonable to 
assume that all these species have been transported to the lake in 
the above-mentioned manner. In my opinion these species have 
developed independently in the lake from a single ancestral form 
(perhaps S. longicauda), which in some remote time has found 
its way to the lake in the above-mentioned manner, and which, 
owing to the altered condition of life and isolation, has gradually 
changed its characters and undergone a divergent development 
into several varieties. These varieties in their turn have at last 
attained the character of distinct species. 
In a similar manner the African species, //yophilus perplexus, 
may have been originally derived from the type species, /. flexi- 
bilis, though the alteration of characters, which has taken place, 
is great enough to distinguish it as a well-marked species. The 
occasional occurrence of two species of the genus Schizopera in 
the two other African lakes, in all probability is due to an acci- 
dental transport from the neighbouring Lake Tanganyika, and 
the same may also be the case with some other Copepod-species 
stated to occur both in that lake and in one or other of the two 
remaining lakes. It may be observed here, that Lake Tanganyika 
in its general physical characters differs from the other two 
lakes. It is extremely long and narrow, in some places exhibit- 
ing very considerable depths, and we have historical evidence to 
prove that its water was formerly somewhat brackish in character. 
Nyasa, it is true, while not so long, is also deep and relatively 
narrow, but Victoria Nyanza is very broad and quite shallow. 
The above-mentioned and other physical and perhaps also bio- 
logical peculiarities of Lake Tanganyika seem to have favoured, 
during a long period of isolation, a divergent development of 
certain species, and this development in some cases has preceeded 
to such an extent as to produce even new generic types, all of 
which, however, have conserved the stamp of their phylogenetic 
relation to other forms occurring in the same lake or otherwise. 
Such highly specialised forms, representing particular genera, 
have been recorded among the Brachyura by Dr. Cunnington, 
and among the Macrura by Dr. Calman. Also among the Cope- 
poda a new generic type has been found, viz., 41 ‘gasiloides, with 
three well-marked species. The phylogenetic relation of this 
genus to the genus Hrgasilus is very obvious, the generic difference 
chiefly consisting in a somewhat retrograde transformation of 
the posterior part of the body. 
A development, in comparatively recent times, of new species 
and even genera in isolated basins, is by no means a unique 
feature exclusively peculiar to Lake Tanganyika. We know of 
similar cases also from other parts of the world. Thus, it is well 
