342 Mr. J. W. Fewkes on a Method of 



mens and preparations and valuable assistance and advice; my 

 thanks are also due to Dr. Albert Gunther, F.R.S., for kind 

 permission to refer to the British Museum Collection, as well 

 as to Mr. E,, Kirk])atrick, in cliars^e of the sponges therein, 

 for ready and effectual assistance in doing so. 



EXPLANATION OF PLATE XVI. 



A. Microciona sti-epsitoxa. 



FiffS. 1 & 2. IMain slceletal spicules. 



Fi(/. 3. Echinating spicule. 



Fifl. 4. Subclavate style. 



Fif/s. 5 & 6. Loug toxites. 



Fiff. 7. Smaller form of toxite. 



Fif/. 8. Long toxites ; from a photograph, to show central twist. 



Fif/s. & 10. Isochelte, front and side views. 



[Figs. 1-7 magnified 200 diameters ; figs. 9 & 10 magnified 

 850 diameters.] 



B. Trachytedania (?) echinata. 



Fir/. 1. Main skeletal spicule. 

 Fig. 2. Echinating spicule. 

 Fig. 3. Tjlote spicule. 



[Figs. 1-3 magnified 260 diameters.] 



XLIV. — On a Method of Defence among certain Medusce. 

 By J. Walter Fewkes *. 



The Siphonophora, in common with other Medusse, as is well 

 known, possess a very powerful organ of defence in the sting- 

 ing-cells, also called lasso-cells and nematocysts. There is 

 reason to believe that there may be at least one other method of 

 protection adopted by these animals. I propose this evening 

 to lay before you the evidence of the existence of tliis second 

 method of defence made use of by these animals, and to open 

 the discussion of the homologies of the structures in which 

 this new means of protection is lodged. 



It may be well to anticipate what follows by the statement 

 that the new method of defence is that of discolouring the 

 water by the emission of coloured pigment from certain chro- 

 matic cells on the bracts, and that these cells bear relation- 

 ships and perhaps are homologous with the nematocysts in 



* From the Proc. Bost. See. Nat. Hist. vol. xxiv. pp. 200-208. 



