DAILY MIGRATIONS OF COPEPODS. 
107 
the thoracic feet, and that during this operation the antennae are held as rigid as 
possible at right angles to the chief axis of the body. As MacBride remarks, the 
extended leaps are carried out with such quickness that the parts taken by different 
appendages can not be directly observed, and his conclusion, therefore, is based on 
inference, not on direct observation. But direct observation is not the only means of 
ascertaining how the leap is accomplished. It is an easy matter to render copepods 
quiescent by putting them for a few moments in sea water containing a very little 
ether. Such animals recover on being placed in ordinary sea water and act in all 
respects normally. With a sharp-pointed knife it is possible to cut off the anterior 
antenna? and expanded tail ends of etherized Labidocera?, though the other parts are 
too closely attached to the body to admit of easy removal. Animals from which both 
anterior antennae and the tail have been removed have been kept a day or more after 
recovery from ether and their movements observed. They swim with great agility 
and seem quite as vigorous as normal specimens, but they seldom live beyond IS hours 
after the operation. In their locomotion they show only one type of movement, the 
uniform rapid creeping. This is modified now and then by becoming somewhat 
uneven, but in no instance have 1 observed a Labidocera without anterior antenna? 
and tail take even a short leap. 
Since in these specimens the thoracic legs are sill intact and yet no leaps are made, 
I feel certain that these appendages are not used in the way that MacBride supposed. 
A Labidocera from which the anterior antennae have been removed makes leaps that 
differ from the normal ones only in being somewhat shorter. If, now, the tail of 
such an animal is removed, the animal ceases to leap. Thus the tail is unquestionably 
connected with this method of locomotion. A Labidocera from which the tail has 
been removed can likewise leap, though in this case, also, the leaps are shorter 
than the normal ones. When, however, the anterior antennae are also removed the 
leaping ceases. Thus the anterior antennae, contrary to MacBride’s opinion, are, in 
Labidocera mtiva at least, connected with leaping. In this species, then, the leap is 
performed almost exclusively by the combined action of the anterior antennae and 
the tail; and the thoracic and other appendages, though they may aid it, are not 
capable in themselves of carrying it out. Since the anterior antenna? and the tail 
are not in action when the animal is creeping rapidly through the water, this motion 
must be ascribed to the action of other parts, probably the thoracic appendages. 
From the preceding account it might be inferred that the female Labidocera' 
retain their positions at the surface of the water and the males keep from accumu- 
lating on the bottom by incessant muscular activit\ T , whereby they lift themselves 
against gravity; but, though this is in large part true, it is not entirely so, for it is a 
most usual occurrence to find both males and females attaching themselves to fixed 
objects, such as the sides of a glass aquarium. This they can do even when the glass 
is so tilted that they are well on the under side of it. If such a suspended animal be 
approached by a sucking tube the current of water that can thus be produced may 
be made to swing the animal back and forth on its support, and it can then be seen 
that the only parts in contact with the glass are the anterior antenna?. Not only is 
this so, but a careful adjustment of the strength of the current will often partially 
loosen the animal, so that for a while it hangs in the water with an attachment to the 
glass by only the tip of one anterior antenna. It is really remarkable with what 
success an animal thus almost completely loosened from the glass will still retain its 
hold. That the other appendages are not concerned in thus anchoring the animal is 
