1880. ] The Siphonophores. 629 
Another question no less significant than the first is, as to how 
we know that the different appendages along the axis are indi- 
viduals and not organs. Why not look upon them simply as 
organs? To answer this question we get some light from a study 
of animals allied to Agalma. There are tubular jelly fishes in 
which the appendages to the stem are not so numerous as in 
Agalma, and where there are clusters of appendages at intervals 
along the stem. Each one of these clusters, however, is com- 
, Posed of all essential members to fit it to lead a separated exis- 
tence. We have in each a necto-calyx, a covering scale, feeding 
polyps with tentacle, and sexual organs. These clusters are 
bound together by the stem, and at a certain age in the life of the 
colony the stem breaks midway between two clusters, which swim 
about as separated individuals which live long enough to 
change their general form. In these genera we certainly have 
a composite animal composed of smaller clusters, each one of 
which isa colony. In Aga/ma that fact is masked, since the 
different component parts are pressed so closely together on the 
axis, but it seems none the less certain that the Agalma is com- 
posite. If we take the different parts which compose one of these 
colonies, many of which joined together form the Agalma, we 
find a resemblance to a typical hydroid medusa in each of its 
component parts. In the necto-calyx we have a hydroid medusa 
where tentacles and proboscis are wanting; in the sexual bells 
we find the same likeness where bell and proboscis are present 
and tentacles fail. The covering scale, polypite and tentacle 
together make up another, and so on. All closely resemble a 
common type of hydroid medusa. Embryology will shed much 
light upon this question, which I shall again discuss. 
From what the anatomy of Agalma teaches, we may conclude 
that we have in this animal the follawing polymorphic individuals 
whose homologous parts “iter se” and with a common Lizzta — 
are given below: 
Lizzta, Bell, Tubes of the bell. Proboscis. Tentacles, 
AGALMa, 
ist individual, Float. TURE REAM tee: ‘ 
ad re Necto-calyx. pres’d by lass lls (4.) 
3d n Covering scale. kiris iii Polypite. Tentacles, {c.d,) (e.) 
4th T Covering scale. di kd scale. Taster. Thread-like tentacles (c./.) (e.) 
ie iy Bell, resent, ? Proboscis with ova. ———————— w) ` 
=i Proboscis with sp (g.) 
S Bell, 
Doubtfully I add to those given 
7th individual, Iny volucrum. = ————— Sacculus. 
The first individual is never duplicated; the remaining are 
