The Tanganyika Problem Reviewed 467 



transported from a marine to a freshwater environment, 

 a change that at least seems serious to the writer. He be- 

 lieves that a natural explanation can be got, which is in line 

 with the exhaustive studies of C. B. Wilson on the Argu- 

 lidae and related organisms, (2(?7 : 25 ( 1903) ; 28(1905); 

 3i(i907);33(i9o8); 39(1911).^ 



This author shows that, starting with such free-swim- 

 ^ ming freshwater types as the Cyclopidae, a progressive 

 series of organisms can be traced which tend to become 

 increasingly parasitic, and so correspondingly condensed 

 and degraded. Thus the Argulidae, Caligidae, Trebinae, 

 Euryphorinae, Pandarinae, Ergasilidae, and Lernaeopod- 

 idae show transition from a free facultative parasitism on 

 the skin or gills of fishes to a complete parasitism on the 

 latter groups, with corresponding simplification of structure. 

 Now according to calculations by the writer the majority 

 of the Argulidae are, like the Cyclopidae, freshwater organ- 

 isms, and are either free-swimming or parasitic at will. 

 Further as emphasized by Wilson, some attach themselves 

 to anadromous fishes, and so may become themselves ana- 

 dromous. This again would gradually lead to a continuous 

 marine life, as is now true of some Argulidae, most Calig- 

 idae, and the majority of the more degraded groups. But 

 the continued existence of degraded freshwater species on 

 freshwater fishes, indicates to the writer the primitive 

 origin and persistent habit of the entire series. This ex- 

 actly corresponds also with the history of the fishes on 

 which they have become holoparasitic. 



Now Cunnington in his "Report on the Branchiura" 

 {2g8 : 262) records 8 species of Argulus from Tanganyika, 

 one of which A. africanus he also gives from Victoria 

 Nyanza, Albert Nyanza and Nyasa. Dolops ranarum seems 

 to have an equally wide range, and is the organism that is 

 known at times to infest frog tadpoles. But a point of some 

 interest is that not a few of the species of Argulus and of 

 Dolops, described by earlier authors, are parasitic on fresh- 

 water fishes of Brazil and the Guianas, not least on species 

 of the Cichlidae. But the writer presents evidence for the 

 view (p. 382), that these and other groups of freshwater 



