POINTS OF THE ANATOMY OP POLYXENUS LAGURUS. 29 



external cuticle and the hypodermic matrix. At the point of 

 insertion of the spine the chitin and matrix are considerably 

 thickened. At the external surface the chitin is raised up 

 round the spine so as to form a rim or ridge (fig. 4) surround- 

 ing a semicircular cup of considerable depth. The hole for 

 the spine to pass through is at the bottom of the cup, and on 

 the internal surface the chitin round this hole projects in- 

 ternally so as to form a short wide tube corresponding to the 

 semicircular depression on the external side (fig. 4, t.). The 

 spine itself is long and rather stout, thicker in the middle than 

 at either end. It is provided with a rim (fig. 4) which fits the 

 perforation at the bottom of the semicircular depression, while 

 the part below the rim projects internally within the tube and 

 ends in a depression, into which a nerve-cell fits. The whole 

 internal part of the organ (i. e. the tube and part of the spine) 

 is embedded in a mass of hypodermic matrix cells, which serve 

 for the renewal of the organ at the moults. On account of 

 the manner in which this organ is adapted to convey move- 

 ments to the sense-cell, and is rather fitted to convey actual 

 pressure than delicate vibrations, I hold it to be a tactile organ 

 rather than an olfactory one. 



With regard to the external generative organs, they have 

 already been described by several authors, but there is one 

 point on which a little uncertainty exists. Fabre describes the 

 male external generative organs as very long, and lying against 

 the abdomen when not in use. Latzel says that they are 

 similar to those of the female, with the exception that they 

 have a round opening and not a slit-like one. I can confirm 

 his account, having had the good fortune to obtain several 

 males among the small number of Polyxenus at my disposal. 

 Sections through the male and female external generative 

 organs are shown in figs. 2 and 3. The dilation of the oviduct 

 into which the external opening passes is shown more markedly 

 than the corresponding dilation of the vas deferens; but I am 

 inclined to believe this is due to differences in preserving. I 

 have noticed that the small, very fine hairs present in both 

 sexes round the external generative openings, are more 



