Prof. E, Cla])arede 07i the Structure of the Annelida. 359 



recent authors, M. de Quatrefages has afresh demonstrated this 

 fact in Eunice, and Dalyell followed step by step the reproduc- 

 tion of a head and branchiee by the posterior extremity of a 

 Sabella^. For my own part I have frequently met with marine 

 Annelida {Eteone, Nephthijs, ike.) which had undoubtedly re- 

 produced their anterior region. The regenerated part is 

 distinguished by a lighter colour and smaller diameter. The 

 aspect of these worms recalls that of the Heteronereides ; so 

 much do the two regions strike the observer by their diffei'ent 

 appearance. One might think them two sections of different 

 worms united together. An interesting question presents it- 

 self in connexion with this : in a worm cut transversely does 

 the posterior part always reproduce a number of segments equal 

 to that of the anterior part which has been suppressed in front 

 of it ? This seems probable. At least I have found an Eteone 

 which had reproduced an anterior section of nearly fifty seg- 

 ments. The head is no doubt the part first formed ; then the 

 new segments are produced successively at the point of union 

 of the old and new parts. This, however, requires to be sup- 

 ported by positive observations. 



Geographical distribution of Annelida. 



This subject, which is still imperfectly known, has only been 

 aj)proached in a positive manner by M. de Quatrefages ; but the 

 data which that naturalist had at his disposal were insufficient 

 to admit of his drawing any very certain conclusions. There 

 is, however, one point upon which I must contradict him, 

 namely the extreme localization of the faunas. For example, 

 M. de Quatrefages does not admit that the Mediterranean and 

 the Ocean can be inhabited by the same species. It sometimes 

 happens that be founds specific distinctions solely upon this 

 circumstance of different habitat, although authors have been 

 unable to establish any morphological difference between these 

 supposed species. He insists especially upon the impossibility 

 of a littoral species supporting conditions of life so dift'erent as 

 those resulting from the presence or absence of tides. At 

 Naples, however, I kept littoral Annelida for months in cap- 

 tivity, and found that the best means of making them thrive 

 is to deprive them of water for several hours every day, so as to 

 allow the mud to become oxygenated. These new conditions 

 did not prevent their living very well and depositing their 



po-o's 



No doubt, in a general way, the fauna of the Mediterranean 



* The powers of the Creator displayed in the Creation, &c. vol. ii. 1853, 

 p. 231. 



