274 ©. H. MARTIN. 
POLYCLADS. 
I have not been able to examine any of the Polyclads 
which have been described as possessing nematocysts, as they 
are unfortunately extremely rare. 
Anonymus virilis has only twice been found by Lang in 
the Bay of Naples. The nematocysts are described as oval 
structures. ‘They are formed in the parenchyme and pass 
along specialised tracts to the surface. They have never 
been seen discharged. 
Stylochoplana tarda.—tThis form, as far as I know, has 
only once been found by von Graff at Trieste. It is interest- 
ing to observe that it only differs from Stylochoplana 
fusca by its slightly smaller size, sluggish habits, and the 
possession of nematocysts. The nematocysts have not been 
figured, but they are said to be over the structures ‘01 mm. 
long with a thread ‘015 mm. long, and a base covered with 
spiral rows of short spines "009 mm. long. In this case it is 
very tempting to suppose that the nematocysts, which are of 
a very common Ccelenterate type, were ingested with the 
food, and that this species is really identical with Stylocho- 
plana fusca. 
CONCLUSIONS. 
There are only three possible views as regards the presence — 
of nematocyts in Turbellaria : 
(1) It might be said that they are absolutely homologous ~ 
structures with the nematocysts of the Coelenterates, and to 
be an indication of the very close relationship between these 
groups (a theory that is put forward in a recent text-book). 
There are, however, several difficulties to the acceptance of 
this view. In the first place no one has yet been able to 
trace the development of a nematocyst in a Turbellarian 
nematoblast. And secondly, it would be very difficult to 
show Cordylophoran affinities in the Microstoma from 
Hickling as compared with the Hydroid affinities of those of 
the neighbouring Sutton Broad. | 
