Defence among certain Meduse. 347 
the darkening of the water by it have probably the same 
physiological function as in the Cephalopoda—to protect the 
attacked animal from its persecutors and facilitate the capture 
of food-animals.” 
The character of the “cystons”’ in a genus of Apolemidx 
called Dicymbia is described by Heckel. Each “ cormidium ” 
or cluster of the stem is said to have in this genus a single 
deep-red cyston, and the secreted pigment is accumulated in 
a “ head-like terminal expansion of the distal proboscis, and 
thrown out by a small terminal opening, the anus.” 
In Apolemia uvaria*, which often reaches a great size, | 
have repeatedly observed the so-called “ cystons”’ in speci- 
mens from Villa Franca. Heckel simply mentions the fact 
that each cormidium of this gerus has several cystons, but 
gives no special description of them. 
The eystons of Apolemia are brick-red in colour and easily 
distinguished from the remaining appendagesof the cormidium. 
Their general relationship to the covering-scales may be seen 
in my figure of the axis of the well-known A. uvaria from the 
Mediterranean. I have not seen them discharge their ex- 
eretions t, but the intensity of their colour varies in different 
individuals and in different cormidia on the axis. Although 
I have repeatedly watched the well-known “lana di mare” 
Apolemia, I have never been fortunate enough to discover 
one which ejected colouring-matter from these reddish bodies, 
and have not been able to produce it by an irritation of the 
animals. 
There is a peculiarity in the tasters of the genus Nanomia 
which would seem to have a bearing on the discussion of the 
pigmented bodies of the cystons. 
A. Agassiz, in his description of Nanomia, called attention 
to the pigment at the base of the taster of this genus, which 
he designated as an “oil-globule.” He supposed that this 
body formed the float of the young Nanomia which budded 
from the parent. From a comparison of this oil-globule with 
the float of the adult I have shown that a derivation of the 
young from the adult by budding is improbable. Still oil- 
globules are very conspicuous structures on the stem of the 
Nanomia, and have not been observed by me in other genera. 
Consequently, although the tentacular knobs and most of the 
* The existence of what I have called “ nectotasters” or tentacular 
appendages to the nectostem in Apolemia is not mentioned by Heeckel (op. 
cit.), although it is an exceptional feature in Apolenua. These appendages 
and the stem which bears the nectocalyces of Apolemia are easily seen 
and have been figured and described. Kdlliker speaks of them as the 
“ Fuhler zwischen den Schwimmelocken.” 
+ Bull. Mus. Comp. Zool. vol. viii. no. 7. 
