84 



ftqttattc JLitt 



aquarist with facilities to experiment 

 with such an apparatus with a view to 

 positively: establishing or destroying the 

 worth of the scheme. Any granular food 

 could be used with the same proportional 

 chances of success, depending on the 

 value of its ingredients, that it would al- 

 low by hand feeding. 



"Electric" Fishes 



Certain fishes exhibit peculiar elec- 

 trical phenomena of muscles, nerves and 

 heart, which have given them the name 

 of electric fishes. These have the power 

 of giving electrical shocks from specially 

 constructed and living electrical bat- 

 teries. Our knowledge of their prop- 

 erties has been increased by measure- 

 ments made with a very sensitive galvan- 

 ometer. 



There are in all about fifty species of 

 these fishes, but electrical properties of 

 only five or six have been studied in de- 

 tail. The best known are various species 

 of torpedo, belonging to the skate family, 

 found in the Mediterranean and Adriatic 

 seas ; the gymnotus, an eel found in the 

 region of the Orinoco in South America ; 

 the malapterurus, the raash or thunderer 

 fish, of the Arabs, a native of the Nile, 

 the Niger, Senegal and other African 

 rivers, and various species of skate found 

 in the seas around Great Britain. 



The electrical fishes do not belong to 

 any one class or group — some are found 

 in fresh water, while others inhabit the 

 sea. They possess two distinct types of 

 electrical organs. One closely relates in 

 structure to muscle, as found in the tor- 

 pedo, gymnotus and skate, while the 

 other presents more of the characters of 

 the structure of the secreting gland as il- 

 lustrated by the electric organ of the 

 thunderer fish. Both types are built upon 

 a vast number of microscopical elements, 

 each of which is supplied with a nerve 

 fibre. 



These nerve fibres come from large 

 nerves that originate in the nerve centres 

 brain or spinal cord, and in these centres 

 are found special large nerve cells, with 

 which the nerve fibres of the electric or- 

 gans are connected and from which they 

 spring. Yet the electricity is not gener- 

 ated in the electric centres and conveyed 

 by the electric nerves to the electric or- 

 gan itself. It is only produced, however, 

 so as to give a shock when set in action 

 by nervous impulses transmitted to it 

 from the electric centres by the electric 

 nerves. 



There are few departments of physiol- 

 ogical science in which can be found a 

 more striking example of organic adap- 

 tiveness than in the construction of the 

 electric fishes. In these animals there are 

 specialized organs for the production of 

 electricity on an economical basis far 

 surpassing anything yet contrived by 

 man. The organs are either modified 

 muscles or modified glands, structures 

 which in all animals manifest electrical 

 properties. — Exchange. 



Oceans are the earth's great storehouse 

 of water. They cover some eight-elev- 

 enths of the surface of the earth to an 

 average depth of about two miles. They 

 receive the off-flow from all the conti- 

 nents and send it back by way of the 

 atmosphere. 



The fresh waters of the earth descend 

 in the first instance out of the atmosphere. 

 They rise in a vapor from the whole sur- 

 face of the earth, but chiefly from the 

 ocean. Evaporation frees them from the 

 ocean's salts, these being non-volatile. 

 They drift about with the currents of the 

 atmosphere, gathering its gases to satura- 

 tion, together with small quantities of 

 drifting solids; they descend impartially 

 upon water and land, chiefly as rain, snow 

 and hail. — Needham and Lloyd. 



