Prof. E. Claparéde on 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 branchize by the posterior extremity of a 
Sabella*. For my own part I have frequently met with marine 
Annelida (Eteone, Nephthys, &c.) 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 different 
appearance. One might think them two sections of different 
worms united together. An interesting question presents it- 
self in connexion with this: im 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 
approached 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 he 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 different 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 
eggs. 
No doubt, in a general way, the fauna of the Mediterranean 
— powers of the Creator displayed in the Creation, &c. vol. ii. 1853, 
p- 231. 
