L.M.B.C. TURBELLARIA. 159 
occurs, produced at regular intervals into spinous pro- 
cesses. The use of this organ has not been definitely 
ascertained. It appears possible that it may have some 
use aS an offensive weapon. It this connection another 
member of this family, Gyrator hermaphroditus, (found in 
fresh-and sea-water in this country) 1s suggestive. The 
so-called copulatory-organ is here converted into a stylet 
enclosed in a sheath and provided with protractor and 
retractor muscles. According to Hallez, it plays no part 
in copulation but enables the animal to seize the Entom- 
ostraca upon which it feeds. On approaching one of these, 
Gyrator bends the hinder end of the body (containing the 
stylet) downwards and forwards and stabs its prey re- 
peatedly, which is then taken up by the pharynx. 
Pseudorhynchus bifidus occurred among drift-weed in 
Port Erin Bay. It is also recorded from St. Andrews 
where it was first discovered by Prof. M‘Intosh; and from 
Millport. 
12. Acrorhynchus caledonicus,Clap.(Pl.XIII, figs. 19, 20.) 
Length 1 mm. Body elongate, cylindrical, shghtly 
tapering anteriorly. Colour white with grey blotches, the 
pharynx pure white. The dermal musculature, as in 
most representatives of this family, is very strong, and 
enables the animal to bear compression under a cover-slip 
without rupture. A mature animal treated in this way 
displays the complicated reproductive organs with almost 
diagrammatic clearness. The granule-and sperm-vesicles 
are bound together in a common penial muscular sheath 
which leads into a copulatory organ armed with small 
knobbed chitinous spines. 
This form is frequently obtained among sea-weeds 
between tide-marks at Port Erin, and also occurs at Skye, 
Millport, and Plymouth. 
