258 Dr. R. von Lendenfeld on Guard-Polyps 
cannot be determined. I have never observed a case in which 
a zoéa which had once been caught freed itself again. 
(Juite another picture is presented when a larger animal, 
such as an Annelid, accidentally touches a tentacle. Imme- 
diately all the prehensile filaments are withdrawn; but, on 
the other hand, the urticating batteries at the terminal ends of | 
the large nematophores are projected far out; the tentacles 
also.are concealed ; so that a comparison with the formation 
of a square to resist an attack of cavalry is certainly appro- 
riate. 
I have indicated above that Allman’s statement that the 
urticating capsules were not pushed forth with the other parts 
of the armed animal relates to a particular condition. I 
believe that he must have observed composite guard-animals 
in which the urticating capsules cannot indeed be protruded 
with the prehensile filaments, but certainly by themselves. 
As a matter of course, J am far from assuming any genetic 
connexion between those Ctenophora which possess prehensile 
filaments and the Plumularide; but nevertheless I believe 
that, by the discovery of adhesive granules in Hydroids, some 
light is thrown upon the corresponding and hitherto isolated 
structures among the Ctenophora. As we see in the Plumu- 
laridee that in the development of the composite guard-polyps 
urticating capsules jist appear, and these are then gradually 
replaced “by adhesive granules, we may well assume that the 
adhesive granules represent phylog enetically the younger 
structures. The same causes must produce the same effects ; 
and thus, in the Plumularide as in the Ctenophora, selection 
may very well have converted the urticating capsules in part 
into adhesive granules: we have before us analogous struc- 
tures. 
Chun* and, subsequently, Claust have asserted the homo- 
logy of urtieating capsules and adhesive granules; and I 
believe that, by the observations above described, this inter- 
pretation will be completely established as correct. 
If we inquire, further, to what tissue the cells in which the 
adhesive granules originate are to be ascribed, their great re- 
semblance to dermal glands, such as we know in various 
Coelenterata, must immediately strike one. In fact I do not 
hesitate to refer them to the unicellular skin-glands, and regard 
the adhesive granule, which, like the urticating capsules, only 
-) . . 
acts once and then disappears, as their secretion. 
* Zoolog. Anzeiger, Bd. i. p. 50. 
+ ‘Grundziige der Zoologie,’ p. 297, note. 
