THE NEMATOCYSTS OF TURBELLARIA. 261 
The Nematocysts of Turbellaria. 
By 
Cc. H. Martin, B.A., 
Magdalen College, Oxford. 
With Plate 14. 
Prior to 1903 it was accepted by most zoologists that 
nematocysts were formed in three separate phyla of the 
animal kingdom—in Coelenterates, Turbellaria and Mollusca. 
If it were really the case that the nematocysts which 
undoubtedly occur in these three separate phyla are pro- 
duced by the tissues of the creatures containing them, it 
would be an example of convergence without parallel in the 
animal kingdom. 
For both in Afolids and ‘Turbellaria there are instances of 
individual species containing nematocysts of two or three 
different kinds which are the exact duplicate of similar 
structures in the Coelenterates. 
In all other cases of convergence, though there may be a 
strong superficial resemblance in structures occurring in 
animals widely separate from one another, careful analysis 
shows that the resemblance never amounts to identity, as it 
does in this case. 
As long ago as 1858 Strethill Wright explained the 
presence of nematocystsin Afolids on the hypothesis that they 
are derived from the Hydroids on which they feed, and in 
1903 Grosvenor (8), after a searching investigation, raised 
this hypothesis to the level of an established fact. 
Since it has been proved that the nematocysts of Aolids 
