THE NEMATOOYSTS OF TURBELLARIA. 275 
(2) The presence of nematocysts might be regarded as a 
case of convergence, and if this theory were accepted it must 
be generally admitted that we have here the most remarkable 
and repeated examples of convergence in the animal king- 
dom. In this case again the experimental evidence, in which 
it is shown that Microstoma changes its type of nematocyst 
with its change of food is fatal. 
(8) The one remaining possibility is the transference of the 
nematocysts of a Ccelenterate to the animal which preys 
upon it. The theory which was first established by Strethill 
Wright for Molids. It is clear from what has been written 
above that this last view must be accepted. Since it has been 
shown that— 
(a) The nematocysts of Microstoma lineare are 
normally derived from the Hydra upon which it feeds. 
(b) If the Microstoma is fed upon Cordylophora, Cordylo- 
phora nematocysts are found under the skin. 
(c) The nematocysts of Stenostoma sieboldii are 
derived from the Ceelenterata on which it feeds. 
The same process probably occurs in the other Turbellaria 
with the’ possible exception of Anonymus virilis, and 
therefore the presence of three nematocysts in a Turbellarian 
offers no ground for the generally accepted homology between 
Nematocysts and Rhabdites. 
LITERATURE. 
1. BEpor.—“ Note sur les cellules urticantes,” ‘ Rev. Suisse Zool.,’ vol. iii, 
1895. 
2. Boumic.—‘ Microstoma papillosum,” ‘Zool. Anzeig.,’ vol. xii, 
1889. 
3. CLAPAREDE.—‘ Récherches Anatomiques . . . dans les Hebridés,’ 
1861. 
4, Fuurmann.—“ Die Turbellarien der Umgebung von Basel,” ‘Rev. 
Suisse de Zool.,’ tome ii, 1894. 
5. Grarr.— Monographie der Turbellarien,’ 1882. 
‘“Stenostoma sieboldii,” } ‘Zeit. wiss. Zool.,’ xxx, Leipzig, 
“Stylochoplana tarda,” 1882. 
