Structure and Polarity of Electric Motor Nerve-Cell in Torpedoes. 251 



seen by Magini in several cases and ascribed by him to the physio- 

 logical activity of the cell. Coggi contended that this space was due 

 to the strong osmotic action between a fixing fluid and the fluids of the 

 cell. 



The experiment performed by the writer was to place a brain of 

 Torpedo ocellata (No. 21) in some light fluid, 95 per cent alcohol being 

 used. This fixed the tissues, and when sections were cut it was found 

 that the osmotic action had forced all the contents of each nucleus in 

 a centripetal direction, leaving the spaces described by Magini on the 

 outer side. These meniscoidal spaces are not outside of the nucleus, 

 however, but are formed within its nuclear membrane, which retains its 

 rounded shape. All contents of the nucleus take part in the movement, 

 leaving an absolutely vacant space to form the meniscus. 



As text-figure 5 will show, this action is centripetal with reference 

 to the mass of the brain, so that laterally placed cells have the meniscus 

 on their outer lateral side and some placed on the under side of the edge 

 of the lobe have it placed nearly on the ventral side. Magini overlooked 

 these fewer exceptions to the general conditions when he stated that 

 the meniscus was always placed dorsally, in addition to his mistake of 

 assuming that the neurite always left the cell in a ventral direction 

 and that the physiological action of the cell as described by him was 

 dorso-ventral in direction. 



SUMMARY AND CONCLUSIONS. 



The net result of the three gravity experiments on torpedoes Nos. 3, 

 4, and 20 seems to show that the plasmosome is the heaviest body in 

 the nucleus, undoubtedly heavier in actual weight than the chromatin 

 bodies and probably of a greater specific weight than any of the other 

 nuclear organs, with the possible exception of the karyosomes. In 

 young fish this plasmosome seems to have a central or general distri- 

 bution, while in older or larger fish it acquires a constantly increasing 

 ventral orientation, which the writer believes due to its increasing size 

 and weight, together with a less resistant condition of the nuclear 

 content to its slow movement through its mass. It may be said (and 

 the observations, as shown in the table, bear it out) that in the small 

 specimens of Torpedo under 12 cm. in length, nearly all cases show no 

 orientation. From 12 cm. up a slowly increasing and quite irregular 

 orientation in the ventral direction takes place, due to the increasing 

 weight of the plasmosome, and greater or less in amount according to 

 the resistance to its movement offered by the physical condition of 

 the nuclear content. This content must be very slightly modified in 

 its solidity, viscosity, etc., by food, by depth and water-pressure, and 

 by individual variation. Such modification, however slight, would 

 account for the variation in the amount of orientation found in different 

 fully grown fish. 



