252 MR. C. F. KOUSSKLET ON THE POLYZOA [Mar. 5, 



With regard to the question of the origin of the freshwater 

 Polyzoa, I am inclined to agree with Dr. Wesenberg-Lnnd (13), 

 who has expressed the view that all the different groups have 

 wandered from the sea, the Phylactolfemata at an early period, so 

 that their marine ancestors are not now known, and may have 

 become extinct in the sea long ages ago, whilst the freshM^ater 

 Gymnolajmata, i. e. Pcdudicella, Victorella, Fottsiella, Arachnoidia, 

 have immigrated at a much later period, so tha,t they still show 

 some affinity with several marine genera. 



If this conception be correct, it follows that there can be no 

 relationship between the living Phylactolasmata and Gymnolpemata, 

 and still less can there be intermediate forms connecting the one 

 with the other. 



In June of last year I succeeded, with the kind assistance of 

 Dr. Bousfield, in again finding Victorella pavida in the Surrey 

 Canal, London, where it had been obtained some twenty years 

 ago, but not I'ecorded since. A study of this species and of the 

 other known freshwater Gymnolsemata has impressed upon me 

 that, in addition to the absence of statoblasts, they are all pos- 

 sessed of a common character of considerable importance, which 

 they share with a gi'oup of marine Ctenostomata, and which may 

 well denote a certain degree of affinity. In all these forms there 

 is a stolon which expands into a cell or zocecium, at the upper end 

 of wdiich an orifice is formed which may become enlarged into an 

 elongated, moi-e or less cylindrical tube for the protrusion of the 

 polypide. Behind the orifice the stolon, after forming a septum, 

 continues to grow oxit to form another cell a little further on ; 

 then on each side of the cell normally one additional stolon arises, 

 also separated by a septum, to foim new branches, which repeat 

 the same process of cell-formation until the growing point of 

 the stolon is either broken ofi" or becomes atrophied. In this way 

 a zoariimi is produced, foi'ming an irregular network of branches, 

 approximately at right angles to each other. This cruciform 

 mode of growth can readily be obsei-ved in all the species of the 

 following genera, which might be grouped together under the 

 nanre of " Orucifornr Stolonifera" : — 



. Freshwater. 



Pcchidicella. 

 Victorella. 

 Pottsiella. 

 Arachnoidia. 



Arachnidium. 1 n^r . * 

 ^ J. , . \ Marrrre*. 



(Jyimdrceciimi. J 



Plumatella TANGANYIK.E, sp. n. (Plate XIY. figs. 1-4.) 

 Specific Characters. — Zoariurrr consistirrg of clear light brown 

 chitinous tubes, branchirrg, curving, arrd interlacing, closely 



* The marine species JBarentsia misakiensis from Japan, described bj- Dr. A. Oka 

 ill 1895, shows the same fundamental structure. 



