AN ICHTHYOBDELLID PARASITIC ON SAND WHITING. 19 
are seen to be violently hurried in various directions. Some 
are driven into the extensions of the segmental lacunae on 
either side, some towards the ventral lacuna, but the majority 
pass through the openings leading to the contractile lacuna. 
'These are immediately closed by the annular muscle fibres 
(PI. 2, fig. 9, S. m.f-), which function as a sphincter when 
the contractile lacuna begins to contract. This contraction is 
from before backward and the lymph is carried to the lacuna, 
lying in the anal region, formed by the fusion of the dorsal 
and ventral lacunae, whence it flows again into the dorsal 
lacuna. The contraction of the contractile lacuna immediately 
follows the diastole of the intestinal sinus, and the dorsal 
blood-vessel in the testicular region; so that it is seen, in a 
leech freshly taken from an ocean whiting, to take place 
about thirty times per minute. 
In this description of the cycle of the circulation of the 
lymph, it will be observed that the events taking place in the 
ventral lacuna are not mentioned. This is due to the relative 
stagnation of the lymph in this lacuna. Despite repeated 
attempts to find a definite direction of flow in the ventral 
lacuna, I have been unable to observe anything more than 
a great deal of regurgition both in this and the ventral parts 
of the segmental lacunae. Frequently strong currents carry 
lymph corpuscles from the dorsal segmental lacunae far into 
these lacunae, and these, and other corpuscles therein, are 
kept in constant movement by eddies. But there appears to 
be no such definite direction of flow as is present in the dorsal 
and contractile lacunae. 
•Comparison with the Lymph Circulation of other 
Leeches. 
Salensky’s (1906) description of the valve arrangement in 
the side vesicles of Piscicola makes evident the course of 
the circulating lymph in this leech and affords an interesting 
■comparison with the circulation above described. 
In Austrobdella I consider the contractile lacunae, on 
.account of their subcuticular position and pouched character. 
