OBSERVATIONS ON FRESH-WATER POLYZOA. 138 



in shape, lying with tlicir long axes along the equator, ahhoiio-h no 

 sliarp hoiindary can be fixed. From an earlv stage, tliev show difFer- 

 iMicv.s in tlie apj)eai'an<3e of theii" cells and lake quite diiterent dii'ec- 

 tions in their future develo|)nient. The axis jc^ining the centres of 

 these areas corresponds, as Avill be seen later on, with the longitudinal 

 axis of the future polyzooid. With regard to the relation of this axis 

 with tlie longer or shorter axis of the statoblast, there seems to be no 

 constant rule, although in the majority of cases the former cor- 

 responded with the shorter axis of the statoblast. 



In one of the two areas, the cells acquire distinctly cylindrical 

 form, and vacuoles are formed in some of them. In f ict. they soon take 

 the form and character of the cells of the outer layer of tlie endocyst. 

 They liegin to secrete gelatinous ectocyst of a sticky nature, by which 

 means the germinaling statoblast attaches itself to anything it may 

 meet with, be it the wall of an aquarium, floating wood, or shells of 

 other statcjblasts. 



The either area gives rise to the polyzooid. Its cells are of less 

 height and vacuoles develope in them later than in the other area. 

 At alx^ut the middle point of the area, the cells nuilti[»ly, and a group 

 of them sinks into the granular mass below, forming a solid club- 

 shaped b(Mly, which a little later on becomes Ik^IIow by the retreat of 

 its cell« toward the periphery. We have now a hollow closed sac 

 bounded by an epithelial layer of cells and connected with the super- 

 ficial thickened area by means of a very short solid stalk (fig. 40, PI. 

 XX). Soon after, the latter also acquires a limien, and the cavity 

 (fig. 49, PI. XX. prim. /.) of the hitherto closed sac comes to com- 

 municate with the exterior. Some cells of the granular mass lose a 

 part of their gi-anules, and arrange themselves hito a sort of layer on 

 the outside of the sac (fig. 49. PI. XX. Lin. I'pifliy Tlie nuclei of 

 these cells Imtotiic lai'g(M' as the granules lessen in (juantitv. and 



