THE FLORAL WORLD AND GARDEN GUIDE. 177 
organs of touch or sensibility. Hach of these is formed of a delicate 
little sac, which incloses another with a minute cavity in its centre. 
Every one of these curiously-constructed bodies terminates in a very 
delicate hair-like process, and form the supposed organs of touch. 
Amongst each group of these organs are others, but less numerous, 
and differently constructed. Corda named these darts, and considers 
them the organs by which the animal holds its prey. This organ is 
formed of a little, pellucid, oval sac, embedded in the substance of the 
knob, and has a small opening atthe apex. At the bottom of this sac 
Organ of Touch, highly magnified. Prehensile Apparatus, highly magnified. 
(After Corda.)—a, first and 6, second (After Corda.)—a, aperture; 6, epi- 
sac; ¢, minute cavity; d@, terminal dermis of tentacle; c, first sac; d, 
_ filament, second sac; ¢, saucer-like body (vesica); 
J, oval base (hastifer) ; g, dart. 
is asaucer-shaped body, upon which is placed a solid oval granule, and 
this supports a long, sharp-pointed spiculum (sagitta), composed of 
calcareous matter, and is capable of being pushed out and in through 
the aperture, probably by the inflation or contraction of the little 
bladder, to which the oval base of the dart (hastifer), is attached. 
When the Hydra is waiting for its prey, the darts are all pro- 
truded, so that its arms become formidable weapons, furnished with 
their numerous spikes. But, more than this, these spikes appear to 
be poisonous also; for any unfortunate animal once touched by the 
Hydra immediately becomes benumbed, and soon dies, or but slowly 
recovers from its effects. 
The mouth of the Hydra is at the base of the arms, and is fur- 
nished with lips capable both of inflection and protrusion. Their 
structure is similar to that of the arms, but they appear to be en- 
dowed with extraordinary muscular force, considering the size of the 
animal. 
The body of the Hydra is not furnished with either darts or 
organs of touch, but, according to Corda, is covered externally with 
a membrane formed of two layers, and that between it and the 
alimentary canal is a muscular layer, composed ‘of dense coloured 
cells, having the appearance of being filled with minute granules. 
The innermost layer, which lines the whole alimentary canal 
from the lips to the arms, is divided at intervals into folds forming 
numerous compartments. The villi of which this layer is com- 
posed are closely connected with the muscular layer. They are of 
a cylindrical shape, and apparently of two kinds, some of them 
June. 12 
