The Wandering Polyzoon. 85 



tlian a few weeks. But if the fully-developed colony is the 

 object of your search, then in the months of July and August, 

 and even in June, if the weather has been warm, go to your pond 

 and seek ; be not content with merely stooping down and pulling 

 out- the weeds, and examining them in your hands out of the 

 water, for such a search will, in all probability, prove an ineffectual 

 one — it being almost impossible, amid the confervoid growth, 

 to detect the collapsed form of your much-prized Oristatella — ■ 

 but lie flat down on the edge of the bank (the Polyzoa are 

 generally within a few feet of the bank, covered by water vary- 

 ing from an inch in depth to about two feet), and put your face 

 close to the surface of the water, staring " with all your eyes •/' 

 then, with as little disturbance of the water as possible, clear 

 away with your hand the floating weeds and Potamogeton leaves, 

 and examine every submerged stem in situ, just as it grows in 

 tbe water — with much patience and " great expectations." 

 Probably, for a minute or so, you will see nothing like what you 

 want ; but, nil desperandum, continue to gaze, and in all proba- 

 bility you will be rewarded by observing, amid the scum and 

 confervse, an oblong object, feathery and transparent, about an 

 inch in length. These colonies bear some resemblance, when 

 the polypes are momentarily withdrawn, to the well-known 

 gelatinous egg-nidamenta ofLimnceus stagnalis. 



M. Gervais has compared the polypidom, to a piece of 

 chenille, and with good reason ; it would not be easy to find a 

 more apt similitude. And now that you have seen one speci- 

 men in situ, you will find little difficulty in being able to dis- 

 cover several more. When the statoblasts split, which happens 

 in the spring, a single polype emerges ; in a day or two another 

 grows or buds out of this one, then another, and so on till the 

 colony is developed. I have found that all the fresh-water 

 Polyzoa are great devourers of the spores of Algse, of Desmidise, 

 and Diatomaceaa; so let the observer, who wishes to keep 

 specimens alive for examination, take care to give them a 

 bountiful supply of such food. Oristatella is unique in one 

 respect : of all the Polyzoa, whether marine or fresh-water, 

 this alone is capable of locomotion ; the movement is certainly 

 very slow, and not easily noticed. The under surface of a 

 Oristatella colony is like the foot of a gastropodous mollusc. " On 

 this disc, which is contractile, and admits of frequent change 

 of shape," to quote Professor Allman, " the colony adheres to 

 neighbouring objects, or creeps about on the submerged leaves 

 and stems of aquatic plants. From the edges of the disc a flat 

 space extends outwards, passing beyond the external series of 

 orifices in the form of a projecting margin, whose interior is 

 occupied by a series of tubular cells or chambers, visible 

 through the translucent skin, and extending in a radiatory 



