186 SUMMARY OF CURRENT RESEARCHES RELATING TO 



namely Spderpes longicauda Green and SjJ. gultolineatus Holbrooke 

 He gives a list of twenty-one species without lungs or with vestiges 

 only. In regard to the forms with lungs, he divides them into two sets : 

 — (1) those in which the lungs extend to the groin, and measure about 

 60 per cent, of the length of head and body ; and (2) those in which the 

 lungs extend only about half-way between axilla and groin, and measure 

 only from 38 to 45 per cent, of the length of the head and body. 

 Camerano's suggestion that the lungs may be important as hydrostatic 

 organs is noticed, but it is pointed out that the lungless forms are not 

 necessarily obliged to lead a terrestrial life. 



Psychology of Fishes.* — Mr. E. Thorndike describes a simple but 

 instructive experiment with Funclulus, which learned in a short time to 

 find its way about in an aquarium where artificial obstacles, keeping it 

 from the shady corner, were from time to time inserted. The fish., 

 though its fore-brain lacks a cortex, clearly profited by its experience,, 

 and modified its conduct, to suit a situation for which its innate nervous 

 equipment did not definitely provide. In common language, it learned 

 to get out of a difficulty. 



Electric Organ of Malapterurue.f— Mr. F. Gotch and Mr. G.G. Buret 

 have measured the electromotive force of the organ shock, and the elec- 

 trical resistance of the organ of Malapterurus electricus. The fish was 

 anfesthetised by immersion in ice-cold water, and then killed, and the 

 organ removed and kept in a moist chamber at a temperature of 5° C. 

 One minor result was to show that the only excitable structures of the 

 organ are the nerve-endings, the organ discs apart from the nerve- 

 endings being inexcitable. Further, each disc with its nerve-endings 

 constitutes an independent system, and the excitatory charge cannot be 

 propagated from one system to another. The maximum electromotive 

 force for the whole fish must be at least 200 volts. The electrical! 

 resistance of the organ was found to be two or three times greater in 

 the longitudinal than in the transverse direction. 



Habits of Poiypterus.J — The late Mr. N. E. Harrington made some 

 interesting observations on the habits of this little known fish which he 

 studied in the Lower Nile. It lives in the deeper depressions of the 

 muddy river-bed, but is an active swimmer ; it swallows living Siluroids- 

 and other Teleosts. In swimming it moves its head freely from side to- 

 side • there is no evidence that it uses its fins for walking or crawling* 

 Although the fish was not often seen taking in air, there is evidence- 

 that a respiratory function is possessed by the swim-bladders or lungs, 

 e.g. the marked peristalsis observed making its way along the larger 

 (right) lobe when the fish is opened alive. 



There are many reasons for believing that the fish does not migrate 

 to salt water, e.g. a slight increase in salinity lulls it. The males are 

 smaller than the females and much less numerous. The breeding time 

 is probably during or just after the inundation of the Nile. The anal 

 fin of the male is used as a copulatory organ. 



There is great practical difficulty in keeping Polypterus in confine- 



* Araer. Nat., xxxiii. (1S99) pp. 923-5 (2 figs.Y 

 t Proc. Eoy. Soc. London, lxv. (1900) pp. 434-45. 

 + Amer. Nat., xxxiii. (1899) pp. 721-8. 



