GEOGRAPHICAL DISTRIBUTION. 75 



most eastern point, while Philadelphia (Leidy, 1. c.) must for the present be viewed as the 

 extreme limit towards the west. 



The species, so far as we are as yet acquainted with their distribution, are thus confined 

 to the North Temperate Zone, not one having been recorded as occurring south of the Medi- 

 terranean in the Old World, or of Philadelphia in the New. It is by no means improbable 

 that they also exist in warmer latitudes, and we cannot but be surprised that they should 

 have escaped the explorations of the numerous naturalists who have examined the regions 

 lying further towards the tropics. We know that the fresh-water tanks in India have been 

 subjected to examination, both botanically and zoologically ; and though we should naturally 

 expect to find the fresh-water Polyzoa luxuriating in such a habitat, none of the naturalists 

 who have described the productions of these reservoirs make any mention of them ; and yet 

 the species of SpongiUa which abound there, and whose European representatives are so 

 frequently found associated with Polyzoa, have . been made the subject of interesting and 

 elaborate investigations. 



The United States of America appear to be especially rich in the fresh-water Polyzoa ; 

 and when we bear in mind, that it is but lately that these animals have received the attention 

 of American naturalists, while but a small portion of that part of the world has hitherto 

 been examined with special reference to them, and that nevertheless — though all the European 

 species have not yet been recorded as living there — two entirely new generic types have been 

 brought to light, while many of the species found present a state of luxuriant development 

 of which we know nothing in the Old World, — when we bear in mind all these facts, we 

 can scarcely avoid the belief that North America will yet prove the grand metropolis of 

 the tribe. 



Further facts must be obtained, before we can arrive at any generalisations of much 

 importance regarding the altitudinal distribution of the Polyzoa. All the British fresh-water 

 species occur in these islands at the level of the sea, and most of them have also been met 

 with in our alpine and subalpine lakes. I have found Plumatella repens and P. fruticosa 

 in Lac Leculejo in the Pyrenees, at an altitude of 4-590 feet ; and P. repens in Lac d'Aul, 

 another Pyrenean lake, at an altitude of about 6500 feet, which is the greatest elevation at 

 which any Polyzoon has as yet been recorded. 



The depth at which the fresh-water Polyzoa occur in the waters frequented by them is 

 never considerable. I have met with PhmateUa jugalls attached to the long petioles of 

 Nymphaa alha, in the waters of a sluggish canal, at about four feet below the surface ; but in 

 most instances, the fresh-water Polyzoa will be found at much less depths, and frequently at 

 the very surface, attached to the under side of floating leaves, or upon the .stones at the margin 

 of lakes, where they are exposed to the ripple as it breaks upon the shore. 



