408 MR. H. A. BAYLIS ON A 
part (through the lappets of the suckers) it has a transverse 
wmeasurement of 0°36 mm. Its width behind the suckers is 
0-28 mm. The suckers are 0°22 mm. long, and 0:15 mm. broad 
in the middle of their length. 
There is no rostellum, and no hooks. 
Text-figure 1. 
Head of Tetrabothrius strangulatus, X ca.70. 
Ex. Aperture of excretory canal (paired). 
All figures were drawn with Abbé’s drawing apparatus. 
The apex of the head bears two pairs of curious apertures in 
front of the suckers. These have the form of small, clear, circular 
areas, crossed by a minute transverse slit. ‘They are probably 
apertures of the excretory canals, fine branches of which can be 
seen passing up to the openings in the head. A similar struc- 
ture has been noted by von Linstow in Zetrabothrius heteroclitus 
(7. auriculatus*|. Behind the head there is a sudden sharp 
constriction, forming an isthmus only 0-08 mm. in width. After 
this the width of the neck increases rapidly again to 0:17 mm. 
Segmentation begins at about 0-25 mm. behind the constriction 
the earliest proglottides being about 0°05 mm. long by 0:14 mm, 
* Voyage of H.M.S. Challenger, Report on Entozoa (1884), pp. 14-18. 
