of the Piedmontese Coast. 165 



met with a large serpent, which lay stretched out at full length 

 on a bed of fallen leaves. I at first thought it was dead, and 

 raised it up by the middle with my stick ; but the creature was 

 only basking, and glided away. The peasants said this kind 

 was " molto cattivo ; " but I believe it was only the common 

 snake of an extraordinary size. They also spoke of a small, but 

 very venomous adder, not much thicker or larger than a man's 

 linger, which would dart at, and kill, a dog. In a ravine behind 

 Genoa, where I had been searching for Paludince in a brook, I 

 saw an animal in the water under a large stone, which I at first 

 took for an eel ; but while I was speculating on the singularity 

 of finding an eel in that country, and poking the creature with 

 my stick, it climbed up a rock and escaped into a deep pool, 

 hissing violently and showing a blunt and villainous head. Dr. 

 Gray tells me it must have been a species of TropidonotuSj and 

 that none of the freshwater snakes are poisonous. However, I 

 never got bitten ; and I generally took with me a small vial of 

 sal-ammoniac as a remedy against such a contingency. I also 

 met several times with the disgusting, but harmless, striped 

 salamanders. 



I here received intelligence of the death of my lamented and 

 venerable friend. Monsieur de Charpentier, whose loss (although 

 in the fulness of his years and honours) science has so sensibly 

 felt. I had hoped to pass a few days with him before I returned 

 to England. 



From the Lago Maggiore I crossed the Alps by the St. Gothard 

 Pass, and returned home through Lucerne, Basle, Strasbourg, 

 and Paris. Londinum " longae finis chartseque visequet." 



1 will now proceed with the more scientific part of my memoir. 



The extent of the geographical distribution of marine animals, 

 as well as the laws which regulate that distribution, seem to be 

 at present involved in such obscurity, that, although I may not 

 be able to throw much light on the subject, any additional facts 

 which I can adduce will, I am confident, be useful in assisting 

 others in time to solve this difficult and interesting problem. 



In considering this subject it is necessary, in the first place, 

 to say a few words as to the definition and limits of what natu- 

 ralists call " species." 



The question whether a species exists in the scale of nature, 

 or not, has been much discussed. Most naturalists maintain 

 the affirmative. In the earher stage of natural history it seems 

 indeed almost absurd or supererogatory to doubt the existence 

 of species ; the number of objects presented for examination and 

 comparison being few, and easily distinguishable by certain defi- 

 nite characters. As science however advances, the number of 



