INTRODUCTION. 
7 
“ for,” says Muller, “ they seize hold of them while 
swimming, by their feet, and daintily suck the life’s blood 
out of then’ captives with their sharp beaks.”* * * § “ The 
Hydreef also, and not a few aquatic larvae, lay snares for 
them, and many Vorticellae frequently grievously infest 
them, for they not only adhere, often in heaps, to the mem- 
bers projecting beyond the shell, but also, nestling them- 
selves within the shell, they overspread the whole body 
with their own colonies, not a little retarding the motion 
and agility of their host.”J The larva of the Corethra 
plwnicornis , known to microscopical observers as the 
skeleton larva , is exceedingly rapacious, more especially of 
the Daphniae. They seize their prey with the rapacity of 
a pike, grasping it with its two strong jaws, and gorging 
them alive. § Pritchard says they are the choice food of a 
species of Nais, which he calls the Lurco , and which de- 
vours them in great numbers. || The Chydorus sphericus 
is their especial favorite, and I have repeatedly verified 
Pritchard’s observations, having counted at least ten in- 
dividuals swallowed alive, and lodged in the different 
stomachs of this glutton. Those in the first and second 
stomachs were still ali ve, while those contained in the in- 
* Entomost. p. 8. 
f “It would appear that there is something eminently poisonous to 
animals in the fresh- water Hydrse. ‘I have sometimes,’ says Baker, f forced 
a worm from a polype the instant it has been bitten (at the expense of 
breaking off the polype’s arms), and have always observed it die very soon 
afterwards, without one single instance of recovery.’ To the Entomostraca, 
however, its touch is not equally fatal for I have repeatedly seen Cyprides 
and Daphnise, entangled in the tentacula and arrested for some considerable 
time, escape even from the very lips of the mouth and swim about after- 
wards unharmed — their shell evidently protecting them from the poisonous 
excretion.” — Johnston, Brit. Zooph., 2d edit., p. 131. 
% Loc. cit., p. 8. They are frequently covered completely with a small polype, 
called by M. Ileamur “Polypes a boucjuet;” for an account of which see 
Trembley’s ‘ Memoire sur l'es Polypes a bouquet, a la suite des decouvertes 
de Needham,’ Leyde, 1747 ; also De Geer, ‘Hist. des Ins.,’ vii, 437, where 
he informs us that in April 1742 he first observed this fact, and made a re- 
port upon it to the Academy of Sweden, which that learned body inserted 
in the Memoirs of the Academy in 1747, previously to Mr. Trembley’s work 
being published. 
§ Brightwell, Zool. Journ., v, 396 ; and t. xix, f. 1. 
|| Microscop. Cabinet, p. 81. 
