AN AFRICAN MEDUSA. 75 



of this species appeared to be somewhat larger than those of 

 L. tanganicce. This statement is correct also with regard to the 

 specimens from the Norquane River. A number of the sense- 

 organs from different individuals of L. rhodesice were measured 

 with care, and the average diameter found to be 135 ja; exami- 

 nation of preparations of L. tanganicce showed the diameter of 

 the sense-organs of this species to average 70 it and not to 

 exceed 90 li (at least in the few specimens at our disposal). The 

 latter measurements were taken from some medusae collected by 

 Dr. Cunnington in Lake Tanganyika in 1905. 



There seems to be no definite statement as to the size of the 

 sense-oi'gans in any of the numerous descriptions of the Tangan- 

 yika, medusa. Gunther (3), however, figures two of these organs 

 X 1000, which by calculation gives the diameter as 60 /jl, this 

 agrees fairly well with the measurements given above. 



Parasitic Infusorians. — Annandale (15) recorded the occurrence 

 of numerous examples of Trichodina pediculus Ehrenberg on the 

 manubrium of specimens of L. indica. 



A peritrichous infusorian belonging to the same genus was 

 found in great abundance on many of the specimens of L. rhodesice 

 from the Norquane River, occurring not only on the manubrium 

 but also on the velum, the tentacles, and the surface of the 

 umbrella, sometimes in such numbers as to give the whole medusa 

 a spotted appearance when viewed under a lens or a low power of 

 the microscope. Sections of a medusa, showed a number of these 

 infusorians inside the circular canal which runs peripherally along 

 the umbrella-margin ; they showed no signs of having been acted 

 on by digestive juices, and were as well preserved and stained in 

 the same way as those occurring on the umbrella surface : this 

 suggests that Trichodina is able to lead an endoparasitic existence 

 within the gastrovascular system of the medusae. 



The occurrence of Trichodina on both the Indian and Rhodesian 

 species of Limnocnida led us to examine some preparations of 

 L. tanganicce. These revealed the fact that this species also is 

 infested with this infusorian, which in warmer countries therefore 

 turns out to be a, fairly constant associate of freshwater jellyfish, 

 and must play much the same role with regard to these organisms 

 as it does in the case of the species of Hydra in this country. 



Bibliography. 



1. Martens, E. vo^, and Bohm, R. — "Ueber eine Qualle im 



Tanganyika, See, mit Bemerkungen." Sitzgsb. naturf. Fr. 

 Berlin, 1883, p. 179. 



2. Gunther, R. T. — " Preliminary Account of the Fresh-water 



Medusa of Lake Tanganyika." Ann. Mag. Nat. Hist. 

 ser. 6, vol. xi. 1893, p. 269. 

 3. . " A further Contribution to the Anatomy of Limno- 

 cnida tanganyicce." Quart. Journ. Micr. Sci. vol. xxxvi. 

 1894, p. 271. 



