634 ANNELIDA '. TOMOPTERIS ; LUMINOSITY. 



Antennae. At a is represented the earliest Larva hitherto met 

 with, enlarged as much as ten times in proportion to the adult 

 at b ; and here we see that the head is destitute of the frontal 

 horns, hut carries a pair of setigerous Antennae, a, a, hehind which 

 there are five pairs of hifid appendages, b, c, d, e, f, in the first 

 of which, b, one of the pinnules is furnished with a seta. In 

 more advanced Larvae having eight or ten segments, this is de- 

 veloped into a second pair of Antennae resembling the first ; and the 

 animal in this stage has been described as a distinct species, 

 T. quadricornis. At a more advanced age, however, the second 

 pair attains the enormous development shown at b ; and the first 

 or larval antennae disappear, the setigerous portions separating at a 

 sort of joint (g, a, a), whilst the basal projections are absorbed 

 into the general wall of the body. — This beautiful creature has 

 been met -with on so many parts of our coast, that it cannot be 

 considered at all uncommon ; and the Microscopist can scarcely 

 have a more pleasing object for study.* Its elegant form, its 

 crystal clearness, and its sprightly, graceful movements render it 

 attractive even to the unscientific observer ; whilst it is of special 

 interest to the Physiologist as one of the simplest examples yet 

 known of the Annelid type. 



494. To one phenomenon of the greatest interest, presented by 

 various small marine Annelids, the attention of the Microscopist 

 should be specially directed ; this is their Luminosity, which is not 

 a steady glow like that of the Glow-worm or Fire-fly, but a series 

 of vivid scintillations (strongly resembling those produced by an 

 Electric discharge through a tube spotted with tin-foil), that pass 

 along a considerable number of segments, lasting for an instant 

 only, but capable of being repeatedly excited by any irritation 

 applied to the body of the animal. These scintillations may be 

 discerned under the Microscope, even in separated segments, when 

 ithey are subjected to the irritation of a needle-point or to a gentle 

 pressure ; and it has been ascertained by the careful observations of 

 M. de Quatrefages, that they are given out by the Muscular Fibres 

 in the act of contraction, "j* 



495. Among' the fresh -water Annelida, those most interesting to 

 the Microscopist are the Worms of the Nats tribe, which are 

 common in our rivers and ponds, living chiefly amidst the mud at 

 the bottom, and especially among the roots of Aquatic Plants. 

 Being blood- red in colour, they give to the surface of the mud, 

 when they protrude themselves from it in large numbers and keep 

 the protruded portion of their bodies in constant undulation, a very 

 peculiar appearance ; but if disturbed, they withdraw themselves 

 suddenly and completely. These Worms, from the extreme trans- 



* See the Memoirs of the Author and M. Claparede in Vol. xxii. of the 

 " Linnaean Transactions," and the authorities there referred to. 



t See his Memoirs on the Annelida of La Manche, in " Ann. des Sci. 

 Nat.," Ser. 2, Zool., torn, xix., and Ser. 3, Zool., torn. xiv. 



