URTICATING FILAMENTS IN THE MOLLUSCA. 275 



identity Avith tlie similar organs in the medusse, and gave 

 them all the name of urticating organs. 



Since then numerous observations have shown that these 

 organs exist in the entire class of polypes, and in that of the 

 Hydra medusae, as well in the Synaptce, many Turbellarise, 

 some annelids, and lastly, among the mollusca, in some of the 

 Eolidae. 



INIax. Schultze has divided these organs into two cate- 

 gories : one including those of a rod-like form or the bacillar, 

 which are found pretty generally in the Turbellariae ; and 

 the other containing the urticating capsules armed with a long 

 filament. The researches of Johannes Muller, and of Leydig, 

 Max. Muller, and Busch, have shown, however, that this 

 distinction is unimportant, and that all these organs of what- 

 ever kind may be embraced under the common term of 

 urticating filaments, as has been done more particularly by 

 Max. Miiller. Dr. Bergh adopts the same view. 



M. Bergh has devoted much attention to the urticating 

 filaments or cnida of the mollusca which are far less well 

 known than those of the cEelenterata. Even Linneus and 

 O. F. Miiller had recognised, at the extremity of the papillae 

 of several Eolidans a minute sac, readily distinguishable 

 from its Avhite colour. A similar sac communicating with 

 the exterior was noticed, but wrongly interpreted in Tergipes 

 by Forskal, Cuvier, and Oken, and M. de Quatrefages 

 thought that he could recognise in the whitish contents of 

 this sac the structure of bony corpuscles. But MM. Hancock 

 and Embleton soon rectified this error by showing that the 

 sac contained filiferous capsules. Though at first inclined 

 to deny the correctness of this statement, M. de Quatre- 

 fages was obliged to confess his error, and he fell into the, 

 since then, general opinion that the organs in question re- 

 sembled the urticating filaments of other, lower animals. 



The existence of sacs filled with cnida, that is to say, the 

 existence of true urticating batteries, is then at the present 

 day a well established fact as regards the typical forms of the 

 Eolidse, that is to say, in the genera Eolidia, Montagua, 

 and Facel'ma. The profound researches of Dr. Bergh in 

 this remarkable group of Nudibranchiata, have besides re- 

 vealed the presence of these organs in other genera, as 

 Galvina, Coryphella, Phidiana, and Glaucus. Their existence, 

 therefore, may almost be regarded as a family character. 



Dr. BergVs memoir passes in review a great many species 

 of the Eolidae, and contains detailed descriptions of the 

 oiida peculiar to each. In every case the urticating batteries 

 are planted at the extremities of the papillae above the 



