338 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



origin from the nerve cord are approximately the same 

 in all the segments. There is always one pair arising 

 from the connective and two pairs from the ganglion. The 

 first pair comes off from the connective just behind the 

 septum, while of the two pairs originating from the 

 ganglion one springs from the most anterior of the three 

 lobes, just at that point where the connective merges into 

 the ganglion. The third pair is to be found more 

 posteriorly, and usually originates at or near the 

 constriction which separates the first and second lobes of 

 the ganglion. 



These three pairs of nerves all have a similar 

 distribution. They are true lateral nerves, and do not, 

 as in some forms, e.g., most of the Lumbriculidae, arise 

 from the mid-ventral line as a single nerve, and after 

 entering the body wall divide into two branches. They 

 arise, on the contrary, from the lateral part of the cord, 

 but slightly nearer the ventral than the dorsal surface. 

 They pass out at right angles to it, and extend for some 

 distance in the body cavity before plunging into the 

 body wall. 



Histology of the Nervous System. 



In order to get a clear idea of the histological details 

 of the structure of the brain and nerve cord, it is 

 necessary to examine transverse and longitudinal sections 

 of these organs. If the sections are appropriately 

 preserved and stained, the various elements become fairly 

 well differentiated. The two outermost coverings of the 

 nerve cord have already been mentioned, but in sections 

 it can be seen that both the connective tissue sheath and 

 the muscular layer are extremely delicate. The most 

 conspicuous part of the former are the nuclei of the 

 connective tissue cells, and, indeed, in places it is very 

 difficult to identify any other structural details. The 



