22 A MONOGRAPH OF THE 



has been more fully described by the Rev. R. T. Lowe in his very curious genus Peplidia* 

 found on the shores of Madeira. Mr. Lowe's graphic description is of so much interest that 

 we are induced to give an extract of it. " In a glass of sea-water in which this animal lived 

 for more than six weeks, it had the usual habits of a Boris, but with more activity: swimming* 

 about violently when disturbed or when provided with a fresh supply of water, in which 

 operation the hind part of the body, with the crested fin-like tail, is lashed from side to side 

 with a strong and regular sculling motion ; the fore-part, with the head or veil expanded to its 

 full dimensions, being at the same time beat with equal force and regularity in a contrary 

 direction, or obliquely upwards and downwards, stroke for stroke ; these parts (the veil and 

 crest) performing thus alike the office of true fins. At night, especially when thus in motion, it 

 appeared most brilliantly phosphorescent ; the light flashing progressively but very rapidly 

 along the body, especially from all the branchial tufts and the edges of the veil and crest. At 

 other times it remained quiescently adhering to the sides of the glass, or moving slowly up 

 and down, as if in search of food ; seeming to use the veil as a feeler, but with the tentacles 

 reflected. Sometimes it crawled in the usual inverted position along the surface of the water." 

 " Its mode of swimming perfectly resembles that of the larva of the gnat so common in 

 our English cisterns of rain-water."f This is the only account of the phosphorescence of 

 the Nudibranchs that we recollect to have seen. 



The Nudibranchiate Mollusca are very sensitive to external influences, shrinking quickly 

 from contact, and withdrawing their organs on the least sense of danger. When crawling on 

 sea-weeds or corallines, they often detach themselves on being disturbed, and drop to the 

 bottom of the water. The Bolides, when alarmed or irritated, erect their papillae, and 

 sometimes agitate them in a convulsed manner, directing their apices to any source of 

 annoyance ; each papilla being endowed with a motion independent of the others. On such 

 occasions urticating filaments are probably ejected from the tips of these organs. We once 

 had an opportunity of observing fluid emitted from the papillae of JEJolis picta. While watching 

 this species, with the aid of a powerful lens, as it was moving about in a small vessel of water, 

 the animal became suddenly alarmed, raising and twitching its papillae, which at the same 

 instant gave out from their apices minute streams of a milk-white fluid; these curling upwards 

 were dissipated in the surrounding medium, and there can be little doubt contained urticating 

 bodies, which the papillae always eject on slight pressure. The papillae of Eolis, Doto, Antiopa, 

 and some other allied genera, are very slightly attached to the back, and the animals appear 

 to have the power of casting them off voluntarily, in the same manner as a crab throws off its 

 claws, or a star-fish its arms. We have frequently found an JEotis or an Antiojpa that had been 

 injured in capture, or placed in sea-water that was a little impure, throw off the whole of its 

 branchiae in a very short time. It is curious to see the papillae on such occasions swimming 

 through the water like independent worms, propelled by the vibratile cilia, and occasionally 

 by a convulsive motion of the muscles, which do not lose their vital power quite immediately. 

 The organs thus cast off are quickly reproduced when the animal is in a healthy state ; and 

 what seems strange is that, in the mean time, it does not appear to suffer any inconvenience 

 from the loss of these, as might have been supposed, vital organs. Even when they are all 



* This genus we take to be synonymous with Plocamopherus of Ruppell. 

 t 'Ann. Nat. Hist./ v. 11, p. 311. 



