MORPHOLOGY OF MELIBE 523 



The muscles ramifying in the papillae form a sort of supporting 

 wall ; underlying this art^ the hepatic branches (PI. , hg. 25, 

 Cshh), with many transparent spaces between (Osp). On the 

 outside of the muscle-wall, just beneath the ectoderm, are 

 odoriferous glands (Og). The size of the papillae decreases 

 gradually from the anterior to the posterior pair, the last pair 

 being very small, and its hepatic as well as muscular contents 

 are reduced accordingly. Eegenerating pairs of the anterior 

 papillae show a great number of hepatic branches and muscle- 

 fibres ; this is a striking contrast to old posterior papillae which 

 apparently have no muscle-fibres and no hepatic diverticula. 

 It has been observed quite frequently, by different authors, 

 that the papillae of Aeolidia when cast off swim through 

 the water like worms, propelled by the vibratile cilia, and 

 occasionally by the spasmodic action of the muscles (Jeffrey, 

 1869). I have myself kept papillae of Aeolidia, at Woods 

 Hole, and of Her miss en da, at Friday Harbour, alive in 

 glass dishes for weeks at a time, the papillae being in constant 

 motion, swimming in a circle owing to ciliary action on their 

 curved surface. This phenomenon is not so extraordinary 

 as it seems. It is found in other invertebrates (Plan aria, 

 Echinoderms, &c.). Gamble (1892) reports that the 

 papillae of L o m a n o t u s show remarkable co-ordinative move- 

 ments when they are touched gently. Autotomy and regenera- 

 tion of the dorsal appendices, according to Parona (1891), is 

 a common occurrence among T e t h y s and Aeolidia. 

 Pease (1860), referring to M. pilosa, says : ' When slightly 

 disturbed they would cast off one or all of their lobes . . . : they 

 may be consequently reproduced, after being cast off.' This 

 is also true for M . 1 e o n i n a , for it frequently throws off some 

 or all of its papillae, and yet I have kept specimens of this 

 species for a number of days without autotomy taking place ; 

 I have also kept preserved specimens for years without the 

 papillae having dropped off, even though they were subjected 

 to considerable handling (see PI. 27, figs. 1, 2, 3). Lang (1896) 

 also records the fact that if the papillae fall off they are 

 regenerated. It is believed that the papillae serve as organs 



