262 OC. H. MARTIN. 
are extraneous structures it seemed to me that the same would 
probably prove to be the case in Turbellaria, and the follow- 
ing paper is an account of the investigation which I have 
made on the subject. 
The research was commenced in Scotland on Loch Tay and 
Loch Lomond, when I was working on the Scotch Lake 
Survey under Sir John Murray, to whom, for his kindness, I 
am greatly indebted. 
In November, 1906, I had the opportunity of occupying 
the Oxford Table at the Naples Aquarium, and there I was 
enabled to examine some of the Marine 'l'urbellaria, in which 
the presence of nematocysts has been suspected. 
I should like to take this opportunity of thanking the staff 
of the Aquarium, and Professor Dohrn in particular, for the 
great kindness they showed me. 
In April I had an opportunity of showing some preparations 
to Professor von Graff, and discussing the question with him. 
Finally, | should also like to thank Professor Bourne for 
his great help in the preparation of the paper. 
The nematocysts of 'l'urbellaria were probably first observed 
by Oersted (13) in Microstoma lineare but he failed to 
recognise their true character, and described them as 
“ Krugformige Drusen.” ‘They were subsequently examined 
by von Siebold (17) in 1848, and he leaves no doubt as to— 
his recognition of their nature describing them as thread 
cells which ‘“‘denen der Hydra auf ein Haar gleichen 
sollten.” ; 
Hallez (9) described the thread of the nematocysts in 
Microstoma lineare as “‘liquide qui se coagule légére- 
ment au contact de eau,” and put forward in common with 
M. Miiller and Leuckart, the view that rhabdites were 
degenerate nematocysts. ‘he essential difference between 
these two structures lies, of course, in the fact that whilst the 
rhabdite is a solid rod of more or less homoy:eneous nature, 
the nematocyst is a capsule contaiing aspirally rolled thread 
which can be everted under suitable conditions. 
