(Re a 
Fewkes.] 300 [October 1, 
knobs of Rhizophysa. Like the former structures they also arise 
as simple buds, but their subsequent growth is very different. Their 
developed form is characteristic of the genus under consideration, 
and does not bear even a superficial resemblance to the ten- 
tacular knobs of other Siphonophorae. They are larger and less 
numerous than the former. ‘The adult form is well described by 
Gegenbaur, to whose account I refer the reader. He does not men- 
tion the power of progression which one of these has when separated 
from its.stem, nor the grasping power possessed by the different 
branches. Both of these characteristics I have often watched under 
a glass of low power. 
The first stage of this tentacular knob is also a simple bud, but of 
very different natures are the subsequent forms of the two. Fig. 9 
represents the simple spatulate outline in the youngest stage; it is 
devoid of lasso cells, and larger than the younger stages of the other. 
In the former case one of the earliest differentiations was the forma- 
tion of a median or apical cluster of smaller cells; here, however, we 
find an apical depression, as shown in fig. 10. Scattered lasso cells 
have appeared, but in a different position from what we found them 
in the former case. Fig. 11 gives us a view where the depression 
has grown still deeper. 
A new and secondary division now appears, so that, as in fig. 12, 
we have the knob divided into four parts; one large and two smaller 
depressions forming four bifurcations. The lasso cells have clustered 
upon these projections as represented in the figures. The tentacular 
knob now differs little from the completely developed, and subse- 
quent crowth is simply a bifurcation and prolongation of these four 
parts into branches, at the extremity of which is always a black spot, 
as represented in fig. 12. 
There is in this stage a peculiar cell, larger than the rest, which I 
have sometimes thought was an opening, and connected with higher 
organs of excretion or sensation; this peculiar structure appears in 
the angle of the larger branches at the point (A). In the adult it 
is a cluster of pigmentary bodies of dark yellow color, surrounded 
by a wall, or enclosed very much as an otolith. ‘Gegenbaur mentions 
it in his text, but does not figure it. In no fully grown Rhizophysa 
is this structure absent, and in the youngest stages it can be seen as 
a simple, prominent cell. 
T have nothing of importance to add to Gegenbaur’s description of 
the third kind of tentacular knob, except that it does not follow the 
