212 LANGDON. [Vol. XI. 



From the ventral nerve-chain, nerve-fibres, apparently arising 

 from the small ganglion-cells, pass out by each of the nerve- 

 roots into the three nerve-rings. A careful study has not been 

 made of the nerve-fibres going to the muscles, but I have 

 observed that they may arise from any part of a nerve- 

 ring. Other fibres which cannot be told from the nerve- 

 fibres of the muscles pass from the nerve-ring through the 

 epidermal nerves and form the subepidermal network pre- 

 viously described. In no case have these efferent fibres been 

 seen to be connected with any cell in their course from the 

 ventral ganglion to their ending in the epidermis. The sen- 

 sory fibres pass without branching, anastomosing, or changing 

 in diameter, to the central nervous system, which they reach by 

 the same course followed by the efferent fibres in passing to 

 the epidermis. Some of the epidermal nerves contain only 

 efferent fibers, some contain both efferent and sensory ; some 

 have been noticed which contain more sensory than efferent 

 fibres, but it is rare to find one which contains only sensory 

 fibres. Each nerve-ring and each nerve-trunk contains both 

 the sensory fibres and the efferent fibres passing to the epi- 

 dermis. Since the sense-organs are less numerous in the 

 posterior half of a metamere, the posterior ring and its corre- 

 sponding trunk contains a smaller number of sensory fibres 

 than the others. Since the sense-organs are usually larger and 

 more numerous around the middle of each metamere, the 

 middle nerve-ring and its trunk contain more sensory fibres 

 than the others. 



In the central nervous system, each sensory fibre divides 

 into two branches. One branch passes caudad, one cephalad, 

 into the ganglia of the next metameres. Each branch ends 

 freely. Of course it is impossible to trace an individual fibre 

 from its origin in a sense-cell to its ending in the central 

 nervous system, but these sensory fibres can be so readily dis- 

 tinguished from all other fibres that it is easy to identify them 

 in the great nerve-trunks and in the ventral ganglia. The only 

 cells with which these sensory fibres are connected are the 

 sense-cells of the epidermal sense-organs. 



