364 



EVENINGS AT THE MICROSCOPE. 



acontium is but a reservoir for the weapons, — a kind of 

 quiver for the arrows ; and the cinclis is a provision for 

 getting them ready for action : we have not yet looked at 

 the arrows themselves. 



They occur under three principal forms ; and for the 

 investigation of these we shall find it convenient to have 

 recourse to different species. 



The first and most generally distributed form is the 

 Chambered Cnida, as it is also the most elaborately 

 organised. I know of no species in which it can be exa- 

 mined under so favourable circumstances as the pretty 

 Madrepore (Caryophyllia Srnithii) of our south-western 

 coasts ; and, as I have several specimens 

 of that species in my aquarium, subjects are 

 at hand for our investigation. The clear ten- 

 tacles are, as you perceive, crowned with 

 opaque globular heads ; if I should nip off 

 one of these heads, and flatten it by means 

 of the compressorium, you would see it 

 literally composed of cnida, the ends of 

 which project side by side, as close as 

 they can be packed one against another. 



But still larger examples may be ob- 

 tained from the craspeda. With a smart, 

 sudden blow I break the stony skeleton of 

 the Madrepore in sunder — the flesh tear- 

 ing apart also ; and thus I expose the 

 interior of the living animal. A great 

 number of pellucid ribbons are now seen, 

 very much convoluted, which are named 

 craspeda. These are almost composed of 

 large cnida. 



I remove with fine pliers a small frag- 

 ment of one of these ribbons, and placing 

 it between the plates of the compressorium, 

 flatten it gradually till the plates are brought 



CNIDA OP 

 MADREPORE. 



