Observations on British Zoophytes and Protozoa. 159 
contains numerous granules, and this ectoderm is continued 
over the cells, they, like the thread-cells of other animals, 
being buried within it. A still more remarkable error is 
committed by the learned author in describing the cells as 
being able to protrude their lassoes or threads through an 
opening in the summit of the cell and again retracting 
them, and further, in imagining that the threads are in- 
struments of prehension. A very careful examination has 
assured me that what he has m.istaken for protruded threads 
are indeed prolongations of the sarcode of the ectoderm 
analogous to the processes of the Ehizopods, and to similar 
processes which are found over the thread-cells of other 
animals. In Oydippe, however, they more readily retracted 
and extended than in the other cases. 
3. On the Stem-Canals o/Tubularia indivisa. 
In the fourth volume of Agassiz's " Contributions to the 
Natural History of the United States," the author has noticed 
a paper of mine on the stem-canals of this zoophyte, v/hich 
I have represented of equal size, and running along the 
stem within the ectoderm. Having described the canals 
in the stem of Tuhularia Couthouyi, and found one of these 
canals larger than the others, he remarks, We find the 
large and the small channels also in a very closely allied 
species, the Tuhularia indivisa of Europe, sent to us by 
Sars from the coast of Norway ; and if the observations of 
Dr Wright were made upon the same species, then his dis- 
covery, although very interesting, is a partial one." I have 
again repeatedly examined the stem of Tuhularia, and find 
that although one or several enlarged tubes occasionally 
exist, it is by no means of constant or frequent occurrence. 
In this zoophyte there is no ground for stating that it exists 
and constitutes, according to the theory of Agassiz, the 
broad chyliferous cavity of the stem. 
