No. I.] SPHYRANURA OSLERL g 



number of conical bodies, which we regard as tactile organs, 

 and the appearance of which is represented in Fig. 2. At such 

 places one recognizes that the deep surface of the investing mem- 

 brane does not rest immediately on the circular muscles, but 

 that there intervenes a narrow space containing fluid (Fig. 

 10), which is enlarged to form the cavity of the tactile cone. In 

 examples that have been under observation for some time 

 granules are seen floating in this fluid; but in perfectly fresh 

 specimens such granules are not present. The wall of the tac- 

 tile cone is formed by the investing membrane, which is, how- 

 ever, perforated at the apex of the cone to allow of the passage 

 of a tactile hair of 13 or 14 f.i length, to which we have fre- 

 quently traced a delicate fibril traversing the axis of the cone. 

 We have not succeeded in satisfying ourselves that these fibrils 

 proceed from subcutaneous nerves, but we consider such an 

 origin probable. 



The free surface of the cone is, furthermore, beset with very 

 short and delicate hairs ; but we have not succeeded in fixing 

 either these or the principal tactile hairs, although the cones 

 themselves are quite well preserved. Twin cones, such as are 

 also represented in Fig, 2, are not uncommon. 



Sphyranura leads such an active life in comparison with the 

 other Trematodes that one might well look for some nervous 

 structures specially adapting it for this. JSIo eyes are present, 

 such as are evident in larval Amphistomes, and such as have 

 been described in young Polystomes and P. ocellatinn, so the 

 development of a series of tactile organs may be regarded as 

 compensatory. Tlie only observations known to us as to tactile 

 organs in Trematodes are on certain structures described by 

 Fischer^ in the neighborhood of the sexual aperture in 

 Opisthotrema. 



These are possibly of the same character as our tactile cones, 

 although Fischer describes them (from preserved specimens) 

 as local thickenings in the investing membrane, which are pene- 

 trated by an axial fibril terminating in a knob. 



Structures somewhat similar to the tactile cones of Sphyra- 

 nura were observed in a peculiar free-swimming Sporocyst, 

 described by the senior author^ from a single example met 



*Zeit. wiss. zool., XL., 12. 

 ''Amer. Naturalist, XIX., 310. 



