190 
BRIGHTWELL, 
ON NOCTJLUCiE. 
precisely like those of an Amseba ; tliese were shortly after- 
wards withdrawn. The grannies with which the fibrils are 
stndded glide gently np and down the threads. The vacuoles 
may also be seen to change their form and position under 
the eye of the observer^ and sometimes they entirely dis- 
appear in individuals that have fasted for some days 
PI. XII_, fig. 6). They appear to be temporary sacs or 
stomachs^ formed in the sarcode mass as they are required 
for the reception of food^ and ceasing to exist as such after 
the food is digested. The number and size of the vacuoles 
communicate a greater or less degree of buoyancy_, and so 
enable the animal to rise or sink. The mouth of the Nocti- 
luca is probably a mere slit. The form given in fig. 15 may 
perhaps be the oesophagus. The ^pinching ofi:'' a portion 
of the body of a Noctiluca^ described by Dr. Webb^ has been 
repeatedly seen by Colonel Baddeley^ Avho showed me one 
example of it (fig. 10) ; it may^ perhaps^, be an abortive 
attempt at self-division_, failing from the absence of a nucleus. 
" The existence of striped muscular fibre in the Polyzoa^ 
when first asserted by Mr. Busk^ was received with much 
hesitation^ though it is now an established fact. The tail of 
the Noctiluca appears also to me to contain striped muscular 
fibre. Late researches go far to prove that (whatever may 
be the true explanation of the appearance called striation) 
its presence has much to do with the power and rapidity of 
muscular action. The powerful motion of the tail in a 
Noctiluca is very remarkable in so small a creature." 
An examination of the Diatomacese found in the Noctilucae 
has brought to light facts of not less interest than those 
arising from an examination of the animals themselves. 
Professor Smith (in vol. i of his ' Brit. Diat.^) has described 
and figured (see ^B.D,/ p. 27, and pi. v^ fig. 46) what he_, at 
first^ called Triceratium striolatum, and corrected to T, undu- 
latum of Ehr. There appears a pseudo-nodule in the centre 
of the figure given of this species^ but Professor Smith_, in his 
observations on the genus^ p. 26^ observes — "The appearance 
of this pseudo-nodule is probably accidental in the single 
individual from which the figure was drawn." 
I had never seen a recent specimen of T. undulatum till 
ColonelBaddeley'sexamination of theNoctilucse brought many 
under observation. Those prepared in acid showed the pseudo- 
nodule as in Professor Smithes figure^ but a careful examina- 
tion of the material^ subjected only to repeated washings in 
soft water_, brought to light these Triceratia in a connected 
state, and has shown that the so-called pseudo-nodule was 
