244 
NOTES AND MEMORANDA. 
turned into its digestive cavity, whence they were successively 
and slowly withdrawn. As the mouth closes but slowly after 
disgorging, I imagine the swallowing them to have been acci- 
dental; and a similar phenomenon carelessly observed may well 
have given rise to a false interpretation. 
It seems that here we have the true explanation of the occa- 
sional presence of nematocysts in the endoderm, and this expla- 
nation my friend, Mr. T. J. Parker, is now inclined to accept. 
As regards the absence of the interstitial cells from the tentacles 
of Hydra fusca I am not able to confirm him ; on the contrary, 
they are present, though in isolated patches, and not forming a 
continuous network as over the body. I find the best way to 
demonstrate these is, having killed a Hydra extended on a slide 
by letting fall a drop of one per cent, osmic acid on it, to at 
once wash away the acid by a flood of absolute alcohol, and then 
after a few minutes to stain with ammoniacal carmine or picro- 
carmine. If the Hydra is now examined in glycerine under a 
power sufficiently high to focus successive layers, the presence of 
interstitial cells can be made out. Owing to their dispersion, 
the want of them in a section becomes very slight evidence for 
their absence. 
III. On the Anal Respiration of the Copepoda. By the Same. 
In a note on Cyclops read at the British Association I pointed 
out that its respiration was exclusively, anal. I have now made 
out the same in CantJiocamptus (fam. Harpacticidcc) , and Diap- 
iomus (fam. Calanida) . In all three the mechanism is the same ; 
at regular intervals, after the backward sway of the intestine, 
the anal valves open for an instant and then close, giving just 
time for a slight indraught of water after the opening, a slight 
expulsion at the close. The necessary pressure to confine the 
animal seems to interfere somewhat with these movements, some- 
times stopping them if excessive ; hence I refrain from noting 
with illusory exactness the intervals between each respiratory 
movement. 
It is to be noticed that the rectum contains as a rule liquid 
only, the bolus of fseces remaining in it but a short time. By 
endosmose the liquid in the rectum will tend to be at the 
same condition of gaseous saturation as the body fluid around 
it, kept constantly agitated by the backwards and forwards sway 
of the stomach. During the short interval that the anus is 
open an approach to gaseous equilibrium with the external 
water takes place, even despite the very slight movement of the 
water (shown by the little change of place undergone by sus- 
pended indigo or carmine particles). In the absence of any 
other suitable respiratory apparatus, no one can hesitate as to the 
function of the action I have described. 
