402 ELECTRO-PHYSIOLOGY CHAP. 



between each pair of porous canals appear under a high power to 

 consist of cemented lumps. Each disc is surrounded externally 

 by a cuticular membrane which here and there may stand free 

 of the anterior surface. 



According to Fritsch, the construction of the electrical organ 

 out of round discoid plates, which hang " like grapes on their 

 stalks " from the stems of the finest nerve-branches, is seen most 

 plainly in young animals, if a section is spread out in a hardening 

 fluid (1 per cent osmic acid), the intermediate tissue being still 

 relatively undeveloped. From this we may conclude that, in the 

 embryo, " the elements destined to form electrical discs appear 

 as a dense accumulation of cells, between which there is an in- 

 definite intercellular substance, somewhat resembling the strata 

 of unicellular glands, as found in the body- wall of many insects, 

 even in the fully - developed state " (Fritsch). The regular 

 arrangement so essential to function is developed later, and not 

 at all in the peripheral parts of the organ. This is so constant 

 that plates have been found at the posterior end of the organ, in 

 the same or nearly the same plane as the body-superficies, i.e. at 

 a right angle with those lying normally, or even in contact with 

 their posterior surfaces. The inferior activity of the posterior 

 half of the organ, as determined by du Bois-Eeymond, is partly 

 due to these irregularities of arrangement. 



Fritsch also endeavoured to count the electrical plates in the 

 organ of Malapterurus by calculations from sections of known 

 length, multiplied into the total extension of the organ. He 

 found " the number of the electrical discs contained in a longi- 

 tudinal unit of the organ, as compared with those of another 

 specimen of Malapterurus, to be in inverse ratio with the length 

 of the organ in both cases," while in the same individual they 

 are 2 per cent less numerous in the posterior than in the anterior 

 sections. Fritsch estimates the total number of discs in the 

 organ at about 2,000,000. " About 1600 lie in series from head- 

 to tail-end, while a cross-section from the middle of the organ 

 contains about 3000. One cubic centimetre of organ contains 

 about 14,000 in a medium-sized specimen." 



The whole innervating system of Malapterurus exhibits the 

 same anomalies as the minute structure of its electrical organ, in 

 an even higher degree. At the commencement of the spinal cord in 

 the region where the first vertebra is connected with the os occipitale 



