74 GEOGRAPHICAL DISTRIBUTION. 



subalpine lakes or of rapid rivulets, where, by close adhesion to the under surface of stones, 

 they avoid the danger of being carried away by the current of the stream ; while others prefer 

 slowly running rivers or the sluggish waters of canals and ponds. 



They are almost all light-shunning animals, loving the dark and gloomy recesses of the 

 lakes and rivers they frequent, where they may be found beneath the shade of aquatic plants, 

 or attached to the inferior surface of stones, or lurking under the arches of bridges where a ray 

 of direct sunlight never enters ; CristateUa alone delights in exposure to the full influence of the 

 solar beams, and may be seen basking upon the upper side of submerged stones, or creeping 

 over the stems of aquatic plants in the clear waters of lakes and ponds. 



With the solitary exception of CristateUa, they are all, in their adult condition, utterly 

 incapable of locomotion, being then permanently attached to some fixed object ; CristateUa, 

 however, creeps about on the stones and plants of its native lake, and thus affords the only 

 instance as yet known of a truly locomotive Polyzoon. 



Lastly, some are timid creatures, withdrawing into the recesses of their cells on the 

 slightest disturbance, and not again daring to venture forth until a long lapse of time has 

 convinced them that all is once more quiet without ; while others must be roughly handled 

 before they will think of retreating ; and the light-loving CristateUa rejoices in the constant 

 exposure of its plumy crown, no ordinary disturbance will force it to retire, it seems alto- 

 gether incapable of existing, except in the midst of the countless vortices which its ciliated 

 tentacula are for ever whirling around it. 



General Geographical range of the Fresh-water Polyzoa. 



The number of forms of fresh-water Polyzoa which, after careful comparison, I have 

 deemed it right to retain as distinct species, amount to twenty-one in all. Of these, sixteen 

 are British ; and of the remaining five, one has only been described as occurring in the fresh 

 waters of Belgium, while four are confined to the United States of America Of these four 

 American species, two constitute respectively the types of two distinct genera. 



We do not, however, as yet possess a sufficient number of observations to entitle us to 

 advance any generalisation of much value as to the geographical distribution of the fresh- 

 water Polyzoa. The most northern point at which we have any positive information of 

 the discovery of a species is probably the neighbourhood of Stockholm (Baeck, in ' Acta 

 Holm., vii, 1745), while the neighbourhood of Nice (^Risso, 'Hist. Nat. de I'Europe Merid.') 

 would seem as far as is yet known to be the most southern limit of the group in the Eastern 

 Hemisphere, and Philadelphia (Leidy, ' Proceed. Acad. Nat. Sci. of Philadelphia,' vols, v and 

 vii) to be the most southern 1 mit at which we have any record of a fresh-water Polyzoon 

 having been discovered in the Western Hemisphere. Vlademir, in Central Russia, where 

 AlcyoneUa fungosa "was ov\gii\a\\y found by Pallas (Pallas, in ' Nov. Comm. Petr.,' 1768), is the 



