626 The Siphonophores. [ September, 
and tentacular knobs. The tentacle is jointed, very contractile, 
and histologically differs in no respect from the stem. Each ten- 
tacle can be drawn up to the base of its polypite, where it may 
be snugly packed away under a protecting scale, or it can be 
extended and allowed to project beyond the body of the Agalma 
to the distance of a foot or a foot and a-half. When thus ex- 
tended the tentacular knobs are best seen and studied. 
e. The Tentacular Knobs— Each genus of the tubular jelly 
fishes seems to have a characteristic tentacular knob. Agalma is 
not an exception. Although in the adult appended to the tenta- 
cle, they begin their growth from the ciliated base of the polypite, 
and do not bud from the tentacle itself. New buds which are to 
develop into tentacular knobs, are continually forming on the 
feeding polyp, and as the tentacle grows are being continually 
pushed out on its walls. In the earliest history of the growth of 
the knob, even, before the polypite on which it is 
borne is fully developed, we find it with others in 
a cluster, partially coiled up at the base of the 
polypite. At that time there is no tentacle, but sim- 
ply a cluster of partially coiled undeveloped ten- 
tacular knobs. In such a condition they might 
SSA, \ easily be mistaken for a wholly different kind O 
KSW || knob from the adult, and the polyps to which they 
KF are joined might be looked upon as a different kind 
of polypite. I believe them only undeveloped forms 
of the true polypite with tentacular knobs. 
In general outline the adult tentacular knob pre- 
serves a likeness to a Medusa. One portion of it 
may be likened to a bell and another to a probos- 
cis. e bell is represented by an envelope SUr- 
rounding the knob, and we might find the homo- 
logue of the proboscis in the coiled structure within 
this envelope. The bell portion is called the in- 
volucrum; the coiled proboscis, the sacculus. The 
sacculus is of dark crimson color, and ends in two ~ 
Fic. 4.—Ten- Drek or threads, and a sac supposed to be con- — ; 
tacular knob. tractie, The sac lies between the two filaments at 
their point of eras with the sacculus. It has been called a 
food reservoir, or “ Saft-behélter.” This last term has been also 
applied to other structures in the Agadma. iS 
According to Keferstein and Ehlers, the tentacular ose: g 
