494 F. W, GAMBLE AND J. H. ASHWORTH. 



have a stout sheath, and consist of bundles of dehcate 

 fibrilte. They arise from large median cells of the cord, 

 according to Fritsch multipolar, according to Apathy unipolar, 

 and they accompany the dorsal roots of the spinal nerves. 



The most recent explanation of the structure and function 

 of giant-fibres is given by Apathy, who has studied them in 

 most detail in leeches and Lumbricus, but also in Lophius. 

 According to this author, in at least each of the anterior nerves 

 of leeches, there are three large " sensorische Schlauche '* 

 in addition to the usual motor and sensory fibres. These 

 " sensorische Schlauche " may be traced into the fibrous 

 matter of the cord, where they become much smaller. Each 

 divides in a T-like manner, and gives off branches which 

 end in peculiar thickenings, " Endkolben," from which 

 extremely fine fibrils are given off. In Pontobdella, how- 

 ever, there is in each connective between adjacent ganglia 

 a large dorsal and generally median " Schlauch," which ter- 

 minates by divisions as in other leeches. Apathy does not 

 state whether these sensory structures, which he homologises 

 with the giant-fibres of, e. g., Lumbricus, arise from peri- 

 pheral sense-cells, but that practically follows from their 

 course and termination in the cord. Their structure is 

 characteristic ; according to Apathy they consist of neuro- 

 fibrillse embedded in peri- and inter-fibrillar structures, the 

 whole being enclosed in an inner myelin sheath and an outer 

 neuroglial sheath. By their structure and their mode of 

 termination in the cord, the " sensorische Schlauche " are dis- 

 tinguished, according to this author, from the other sensory 

 elements which form bundles, " sensorische Biindeln." Both 

 these sets of sensory fibres are distinguished from the motor 

 ones by the absence of ?my direct connection with ganglion 

 cells in the cord, such as those in which the motor fibres as 

 usual arise ; but in no case does Apathy give any indication of 

 the starting-points for the formation of these sensory tracts. 



In Lumbricus the same distinctions hold good, and it is 

 pointed out that the " giant-fibres " are in fact the central 

 portions of the " sensorische Schlauche." 



