( 24) 



cylindrical shape, although that the fracture is irregular. If these 

 pieces are mounted in glj^cerine/) it is possible, as the spicopal almost 

 entirely disappears from the eye, to judge with certainty in which 

 position the thread is seen, whether oblique or not. Paying attention 

 only to those which are undoubtedly seen in transverse optical section, 

 we found by careful focussing that they were really triangular with 

 the angles cut off. In the second place we studied isolated axial 

 threads. By moving somewhat the coverglass, a quantity of little 

 pieces break off, generally almost transversely. At the same time 

 it can be observed that the little fragments turn over, owing to the 

 movement of the fluid. In this way we saw plenty of them from 

 all sides. With high power (Zeiss, homog. imm.) we found that in 

 this case also the transverse section is triangular. In spite of our 

 astonishment that the axial rod in Tethi/a is triangular we cannot 

 but agree with Bütschli's observations. We did not see varicosities 

 nor sharp restrictions ; normally the isolated rods are perfectly smooth. 

 The diameter remains the same, with exception of the extremities ; 

 these are, in uninjured threads, either sharply pointed or rounded 

 off, according to the well kjiown shape of the styli themselves. 

 Deviations of this rule seem to us to be pathological. 



Not less strange than the shape appears to be, is the consistency. 

 This may be the reason that previous authors so little agree. Whereas 

 we And, after treatment with hydrofluoric acid, thai the free axial 

 threads on one hand are very flexible, so that they cnii form clews, 

 we see on the other hand that in man}' cases they l)reak off at once 

 if touched with a needle. We remarked already that they generally 

 break at I'ight angles to the axis. In a certain sense Bütschli is 

 right, therefore, if he calls them "spröde", but it is by no means the 

 sort of t)riftleness of for example a thread of glass. The consistency of 

 the axial thread can be best compared with agar-agar. Here a certain 

 flexibility is likewise combined with the pi'operty of suddenly break- 

 ing. Similar i)henomena are known (^f gels at a certain point of 

 dehydration. 



The axial rod in Tetluja is, taken as a whole, not homogeneous. 

 First of all we observe, especially in threads stained with iodine, a 

 double contour. This is easily demonstrated on uninjured, isolated 

 threads as well as in transverse sections; in the triangular figure, 

 mentioned above, the Avail is both inside and outside li-iangular. This 

 wall is comparatively thick — about 7^ or Yj of the total diameter. 

 We may consider the axial thread as a tube, tilled with something; 



1) Refractive index n = 1.45Ü8. Ct'. iiilVa. 



