SYLLIS. 193 



form, roundish, of a yellowish-brown colour. Head small, distinct, 

 rounded and entire in front, with four eyes placed in a square, the 

 anterior pair more widely set than the posterior. x\ntenn8e three, 

 elongate, filiform, clothed with minute cilia, unjointed. Proboscis 

 apparently without teeth or other armature. Segments numerous, 

 narrow, incised at their junctions ; the post-occipital with a pair of 

 tentacular cirri on each side, one-half the length of the antennae ; 

 the cirrus of the following segment elongate, antenniform. Feet 

 uniramous, short, entire, armed with a single fascicle of retractile 

 simple unjointed bristles. The superior cirrus longer than the 

 breadth of the segments, obscurely marked with a few transverse 

 lines or wrinkles, but not in any degree moniliform ; the inferior 

 cirrus small, and not projecting much beyond the foot. Tail tapered, 

 tipped with a pair of styles. 



Miiller gave to this annelid the specific name proUfera, because he 

 discovered that the worm could propagate itself by a spontaneous 

 division of the body into two halves, the posterior half acquiring a 

 head before it became separated. A worm in this condition resem- 

 bled exactly two individuals jointed together, the one holding on to 

 the hinder extremity of the other. Midler's disco verjr extended no 

 further ; and we are indebted to M. de Quatrefages for the comple- 

 tion of the wonder. From his researches it appears, that although 

 the two halves, when the process of separation is completed, appear 

 to be alike, and are so in all their external characters, yet otherwise 

 they are essentially different. The anterior half — now an entire 

 worm — continues to eat as before, and conduct itself as any indepen- 

 dent annelid ; but the individual formed by the posterior half is 

 destined solely to the generation of its species. It does not eat ; and 

 its intestinal canal, having become unnecessary, wastes and is atro- 

 phied. As, however, the part contained the whole generative organs 

 of the primary individual, the life of it is prolonged, by self-nutrition, 

 long enough to permit these to mature the numerous ova ; and by 

 their dispersion, and evolution afterwards, the race is continued and 

 multiplied*. The Myrianide discloses a more wonderful history, for 

 of this beautiful worm the posterior half becomes self-divided into as 

 many as six parts, each of them acquiring the cephalic appendages of 

 the original before they take leave and separate themselves. In this 

 condition the worm wanders about with a concatenated train behind 

 of six big-bellied mothers, formed of its own tail in, apparently, a 

 normal stage of development. These portions part in due time, 

 — survive long enough for the maturation of the ova storehoused 

 within them, — and then die in giving them birthf. 



This little worm always kept its antennae twisted up in a spiral 

 manner, so that it was not easy to get a distinct view of their num- 

 ber and location : they differ remarkably from those of the preceding 

 species in their greater development ; and it was easy to see, with a 

 magnifier of no high pow ers, that they were clothed throughout with 

 fine cilia. 



* Ann. des Sc. nat. i. 22 (1844). 



f Milne-Edwards, Ann. des Sc. nat. iii. 170 (1845). 



