POINTS OF THE ANATOMY OF POLYXENUS LAGURUS. 99 
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, 7¢.). 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 38. 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 
