74 Dr. H. Fol on the Family Tintinnodea. 
in 1880-1881, has enabled me to resume this investigation 
at the point where I had left it, and to make a step in advance 
in the knowledge of the structure of these animalcula. 
Some forms occurred which I had not previously met with. 
Some further details of structure were able to be elucidated. 
In the natural sciences method plays a principal part; but it 
is nowhere of greater importance than in microscopical re- 
searches: here the fitness of the investigator consists much 
less in any particular perspicacity than in the art of bringing 
into view the points that he wishes to know. Hence the em- 
ployment of a new method has enabled me to see clearly 
many things which I had previously been unable to see, or 
which I had seen imperfectly and misunderstood. 
I shall consequently have not only to describe new details, 
but also to rectify my former data in several particulars. The 
“ Bibliographical Index” contains a memoir (XI.) which had 
previously escaped my notice, upon an Infusory allied to 
those described by me, as well as some publications, rather of 
a critical than a descriptive nature, which have appeared since 
I prepared the ‘ Bibliographical Index ”’ to my previous article 
[‘ Annals,’ vol. vil. p. 250]. 
Method.—The collection of the Tintinnodea in the sea is an 
easy matter. There is no danger of damaging them at the 
moment of their capture, seeing that their test, into which 
they withdraw at the smallest sign of danger, sufficiently pro- 
tects them. 'They are pretty robust, and swim briskly about 
in the bottles several hours after their capture, and at a time 
when many delicate animals are already dead or disfigured. 
It is not, however, at the surface of the sea or under a bright 
sun that we find them in the greatest abundance. In cloudy 
weather they rise to the surface more readily than in bright 
weather; and in the daytime they are found chiefly at a 
depth of several fathoms. 
For their capture I employed a net of fine muslin of 
a conical form attached to a ring about 50 centim. in dia- 
meter. ‘The bottom of the net presents a contracted opening, 
like that of a weel, which opens at the middle of a much smaller 
net made of silken sieve-cloth with very fine meshes. This 
latter is attached to a ring equilibrated by a fragment of cork. 
This net of silken gauze does not injure the animals at all; 
and it captures at least twice as many as the glass bottle 
which some naturalists substitute for it. It is easy to under- 
stand, in fact, that the impermeable walls of the bottle compel 
the water to turn in its interior, and cause eddies which carry 
out a considerable proportion of the captured animals. 
With creatures so active and so difficult to observe alive 
