154 NEREIS. 



The intestine of a young specimen, shorter than an inch, appeared 

 corrugated by the microscope. 



Few specimens, especially those of larger dimensions, are found en- 

 tire, for rupture of the body is common ; and even when entire, the due 

 proportions are seldom seen, owing to the progress of regeneration, which 

 readily ensues. But perfection may be always ascertained by the forked 

 extremity, which is more conspicuous in this species than in any of the 

 preceding. It is not improbable that the fork is obliterated by the gene- 

 ration of new parts in its vicinity, as the natural dimensions of the ani- 

 mal are augmented. However, this is a subject of difficult explanation. 



This creature constructs a very thin transparent silky tube, from a 

 matter exuding apparently from the whole body. Here it rests, expos- 

 ing the head, which commonly waves from side to side. The tube is 

 strengthened by the incorporation of sand where accessible. When other- 

 wise it remains quite transparent, and it is framed of sufficient width to 

 admit of the animal's reversing itself within. Sometimes the quantity of 

 the secreted matter employed in the covering is copious. 



This is a littoral Nereis ; it retreats from the light, lurking under 

 stones, or in the clefts of the rocks. A very fine specimen was found on 

 raising a large shelving portion of rock, near low-water, where always 

 moist. 



I cannot speak definitely of the propagation of the species. Early in 

 February a mutilated specimen discharged thousands of minute ova ; and 

 early in March, I found a quantity of spawn in a vessel containing a 

 specimen, but not solitary. This spawn consisted of thousands of minute 

 yellowish ova, amidst a thin, faint brown, albumenous matter, of too 

 little tenacity to retain them in connection when the vessel was moved : 

 no development followed. 

 It is not rare. 



PLATE XXII. 



FIG. 6. Nereis versicolor \falgens}. 



7. Head, enlarged. 



8. Posterior extremity, enlarged. 



