SCIENCE-GOSSIP. 



*°5 



A FRESHWATER POLYZOON. 

 By Edward F. J. Bryan. 



npHOUGH wonderful may have been the appear - 

 ance of many of the forms of Polyzoa which 

 the zoologist has viewed, he who has failed to 

 subject to microscopic examination that marvellous 

 animal which inhabits our ponds and rivers— 

 Cristatella mucedo — has missed one of the most 

 gratifying experiences which nature holds out for 

 his acceptance. He may have viewed in countless 

 numbers members of other groups, beautiful in 

 outward form and whose interior members are 

 a source of unmitigated wonder, as examples take 

 the genera, Melicerta and Vorticella, in which 

 are combined a delicacy of formation most truly 

 marvellous ; still when through the microscope's 

 magic lens, he shall have viewed the graceful 

 attitude and perfection of form of a Cristatella, his 

 gratification will be unbounded. 



masses, scarcely larger than a pin's head, and whose 

 peculiar faces, convex on one side and concave on 

 the other, render them particularly noticeable. 

 These are but statoblasts or discs which have been 

 produced by former specimens, and as such are of 

 little importance save that they make the presence 

 of polyzoa in those waters an indubitable fact. 

 Proceeding with our examination we at last 

 discover what appears to be an elongated mass of 

 jelly, on an average slightly over an inch in length, 

 and of a yellowish colour. This is the object of 

 our search, although it is as yet but in its embryo 

 state, and must accomplish its germination before 

 it assumes its most beautiful form. Still further 

 search may disclose the fully-developed specimens 

 which are required for examination. Having 

 discovered their oblong, jelly-like colony, mainly 



1. Cristatella mucedo. 



/— V 



2. A SINGLE POLYP. 



3. The same with 

 tentacles withdrawn. 



What then are the characteristics of this creature 

 which is to call forth such inexpressible tokens of 

 surprise in him who beholds it for the first time ? 

 What are its habits, and the manner in which it 

 passes its existence ? Suppose that it is the month 

 of either July or August, a period when all nature 

 is most widely unfolded from the mantle in which 

 it has lain concealed, and when all ponds and 

 running streams are most suited to be the habita- 

 tion of the thousands of microscopic forms of 

 life which have in the delicate lace-like leaves of 

 the water-crowfoot, potamogeton, and other aquatic 

 plants, their birthplace and home. 



Let us proceed to a pond which we may consider 

 of a likely nature, and stooping down close to the 

 water very carefully examine the stems of the 

 aquatic plants as they are growing in the water, 

 for when plucked out of their native element they 

 present such a tangled appearance as to render the 

 finding of any attached polyzoa extremely difficult. 

 First we may notice some small, round, dark-coloured 



F 



by reason of their feathery exterior, basking amid 

 the tangled growth of conferva; and floating scum, 

 great indeed is the satisfaction with which we 

 transfer this most highly prized of the freshwater 

 polyzoa to our collecting bottle for examination at 

 home. 



Regarding its position in the scale of animal life 

 Cristatella mucedo is, like it neighbours Alcyonella 

 fungosa, Fredrhella sultana, and the Plumatella, in 

 its external form very closely allied to the Hydrozoa, 

 or phytoid zoophyte group ; still, its internal 

 structure renders it identical with the mollusca, 

 more especially, however, with the sub-group 

 Ascidiae, which includes all molluscs of a tunicated 

 nature. Still the Ascidians are not altogether 

 identical with the Polyzoa, for while the former 

 possess a heart and vascular system, the latter are 

 wholly devoid of these important arrangements. 



Examining a colony of Cristatella we find it is 

 about an inch and a half in length, almost oval 

 in form, and of a yellowish-brown colour. The 



