24 Introduction to Animal Morphology. 



a lower homogeneous surface made of the expanded axis cy- 

 linder. This lies on a layer of granular protoplasm lyingdirectly 

 in contact with the disdiaclasts, or no granular layer may in- 

 terpose (Frog). In electric and pseudelectric plates, nerves end 

 in a similar manner. Hettsen describes nerves as ending in 

 the nucleoli of epithelial cells in frog skin ; Lippmann, in the 

 nuclei of the corneal corpuscles ; Joseph, in the nuclei of bone 

 corpuscles. 



Nerves when living are weakly alkaline, or neutral.* 

 After death, or when heated, they become acid; during 

 action they take in oxygen and give out carbonic 

 acid [Raitke). Impressions travel along nerves at the 

 rate of n i feet per secondf [Helmholtz and Baxt)y 

 nearly the same rate as that of a sound wave through 

 a material of equal density. 



CHAPTER V. 



TECTOLOGY. 



Animals, as distinguished from plants, are living 

 beings whose nitrogenous form-elements are con- 

 tinuously united (not separated by partitions of ternary 

 compounds), assimilating organic matter only,:}: ab- 



* Constant electric currents make nerves acid at the anode, but un- 

 changed at the cathode. 



t Danders staXes, the rapidity of feeling as Y', of hearing \", of sight ^". 

 In each of these and the consequent muscular action there are the following 

 stages : — I. Action on the percipient element ; 2. communication to nerve 

 ganglion cell ; 3. increased action in this cell ; 4. conduction to sensorium : 

 5. action in sensorium ; 6. action of volition ; 7. conduction to motor cells ; 

 8. action in these cells ; 9. conduction to muscle ; 10. action of muscle. 

 Tlie psychical part he supposes to occupy about 0.06". 



X Like all organic beings devoid of green chlorophyll, such as 

 Saprophytes. 



