628 



Oesophageal nerves arise close behind ventral commissure and, 

 while still connected with brain lobes form a delicate commissure; 

 a few sections farther back a second stouter commissure occurs be- 

 tween the two nerves. The lateral nerves lie outside of the outer cir- 

 cular muscle in the head region, in and then within the outer circular 

 muscle in the forward part of anterior intestinal region , finally they 

 come to lie in the longitudinal muscle, and continue in this position 

 to the end of the body. 



Dermal sense organs : twelve small sensory pits are found on the 

 dorsal surface of the head in the median line. The first occurs eight 

 sections behind the tip of the head, the twelfth, above the ventral 

 commissure. The sense organ is a circular pit (s. p. Fig. 1), sunken 



e.p. 



sp 







m.fr 



Fig. 1. (Zeiss Oc. 4., Obj. D.) Transverse Section of Sensory Pit. e.p. epithelium, 



s.p. sensory pit, cm. circular muscle fibres, l.m. longitudinal muscle fibres, 



b. I. basement layer, m.f. muscle fibres. 



below the surface of the skin, in which are long slender cells with 

 nuclei at their basal ends and terminating in long cilia. I have not as 

 yet been able to trace the innervation of the sensory pits, except in 

 one case where I observed a nerve arising from the dorsal commissure 

 and running dorsally, towards the pit above it. 



Blood system: four lacunae communicating in tip of head farther 

 back become two, which unite in a ventral commissure in brain region. 

 From the ventral commissure, the two lateral trunks and an unpaired 

 median ventral branch, oesophageal vessel, arise. The oesophageal 

 branch soon divides into two vessels which reunite with the lateral 

 trunks behind the mouth. The two »lateral rhynchocoel vessels« arise 



