POLYZOA OF WATERWORKS. 451 



intimately connected with one another, and are therefore like 

 the form which has been described as var. co7'aUoides. 



Braem (90, p. 4) has stated that the floating statoblasts of 

 P.fungosa (typical form) have an average length of 410 /x, and 

 an average breadth of 320 |U ; the corresponding measurements 

 for var. condloldes being respectively 380 /.i and 300 f.i. In my 

 own material the average length of eleven floating statoblasts, in 

 one series of measurements, was 371 ^ ; and the average breadth 

 was 240 ju. The extreme measurements were : — Length, 328 /j and 

 416 M ; breadth, 224 /u and 264 ^u. In another series of measure- 

 ments, in which the statoblasts of the compactly arranged tubes 

 were distinguished from those of the peripheral, more coralloides- 

 like tubes, the average length was 388 jj. and the average breadth 

 rather more than 280 ju * for the former ; while for the latter the 

 length was 358 jj. and the breadth was 266 /li. There is thus some 

 difference between the sizes of the statoblasts in different parts of 

 the same mass of tubes ; the looselj'' arranged zooecia at the 

 periphery having somewhat smaller statoblasts than the more 

 centi-ally placed ones. But even the largest statoblasts agree 

 more closely in size with those of var. coralloides (from Braem's 

 measurements) than with those of the typical fimgosa-iovui (as 

 given by the same author). I refer the specimens, therefore, to 

 var. coralloides ; and this conclusion is confirmed by the measure- 

 ments which I have made of a very typical fungosa-iovm. from 

 a pond at Upper Norwood (Brit. Mus. 85.7.28.5-8), in which 

 the average length of the floating statoblasts was 431 fx, and the 

 average breadth 307 ij. : in close agreement w'ith Braem's figures. 



The floating statoblasts of the material from Styche have the 

 form shown in fig. 22. They do not vary much in form, although 

 in some of them one of the sides is more convex than the other. 

 The annulus leaves a considerable part of the central capsule 

 exposed on both surfaces of the statoblast. The average ratio of 

 length to breadth (11 cases) is 1*543 : 1. 



The sessile statoblasts are considerably larger than the floating 

 statoblasts. On the attached sxirface (fig. 23) the central capsule 

 gives off an irregular peripheral ring of cementing substance, 

 which forms a vertical ridge by which the statoblast is fixed to 

 the wall of the tube in which it has been produced. On the free 

 surface (fig. 25), a saucer-like shape is produced by the develop- 

 ment of a thin marginal collar. This I'epresents the annulus of 

 the floating statoblasts, as is shown by its structure. 



In some statoblasts the gas- cells are represented by only a small 

 proportion of the number found in a floating statoblast ; and these 

 occur in isolated groups, of irregular and obviously inconstant 

 form (fig. 25). In other cases, as in fig. 24, the annulus forms a 

 complete band, which is almost as well developed as in the floating 

 statoblasts. 



* The uncertainty about the breadth is due to the fact that the statoblasts 

 measured were not resting accurately on one of their flatter surfaces. 



Pkoc. Zool. See— 1913, No. XXXI. 31 



