and Urticating Cells. 257 
battery ; and these in older guard-animals attain the form and 
size of adhesive granules. At the same time the number of 
enidoblasts diminishes, the urticating capsules falling out and 
the plasma-envelopes degenerating. Frequently, however, a 
few urticating capsules are found even later in the head of 
the prehensile filament, and these are not thrown off until 
very late. In the older parts of the stock they never occur. 
Allman states* that in some Plumularide, and especially in 
Antennularia, the nematophore is divided into two stories by 
a diaphragm. I can confirm this statement for the Australian 
Antennulartie ; and add that in many (perhaps all?) species of 
Aglaophenia also such a diaphragm is more or less developed 
in the paired superior nematophores. 
The division of the body of the nutritive polyps of the 
Plumularide into an oral and an aboral half, which is caused 
by a considerable circular constriction in the middle of its 
length, has already been described by Hamannt. His state- 
ments apply also to the Australian species. ‘he division of 
the large guard-polyps into a distal defensive and a proximal 
offensive half seems to me to indicate that in this case the 
centripetal part is homologous with the aboral and the centri- 
fugal with the oral part of the nutritive animal. 
I have frequently had the opportunity of tracing in the 
living animal the mode of action of the armed animal, and 
will here give the most important points. The Aglaophenicee 
live principally upon zoée and other larve. If a zoéa comes 
in contact with a tentacle it is struck by several cnidocils and 
makes vehement movements in order to escape. ‘These efforts, 
however, are fruitless, which I would ascribe to a numbing 
action of the nettling threads. As soon as the zoéa has 
touched the tentacle, all the prehensile threads (there are five 
of them) belonging to the particular polyp bend and stretch 
themselves towards the spot. Usually the zoéa at the same 
time touches the adhesive head of one or other of the prehen- 
sile threads and adheres to it firmly. While the prey-loaded 
filament rapidly shortens, the zoéa, which makes very strenu- 
ous movements, soon sticks to several prehensile filaments, 
which shorten as soon as they are touched. The zoéa is 
quickly so surrounded that it can no longer move. In this 
state it gets again within reach of the tentacles. ‘The separa- 
tion from the head of the prehensile filament is effected by 
the casting off of the adhesive granules. Whether a poison- 
ous action is to be ascribed to the adhesive granules also 
* ‘Monograph of the Gymnoblastic Hydroids,’ vol. i. p. 28. 
+ Jenaische Zeitschrift &c. Bd. xv. p. 57. 
