Form of Freshwater Coclenterate. 115 



corresponding to tlie above-mentioned thirty- two buds. The 

 separation of the thirty-two parts of the parasite generally fol- 

 lows a regular course, {, e. the complete spiral turns (each con- 

 sisting of eight buds) first of all separate ; these small chains 

 are then successively halved, so that we get pieces representing 

 four and then two buds, and then finally thirty-two isolated 

 individuals. 



Soon after the appearance of the secondary buds these in 

 growing change their rounded pyrifovm shape, become angular, 

 and acquire the form of two low trapezia with their bases 

 placed together and resting upon a cylindrical pedestal (the 

 peduncle). The anterior or upper trapezium, with the 

 longitudinal groove (the upper division of the bud) which 

 bears the twelve secondary tentacles, corresponds, as I have 

 already remarked, to the aboral extremity of the future free- 

 living form (mother). The hinder or inferior trapezium, on 

 the other hand, which rests upon the cylindrical peduncle (the 

 lower part of the bud) and which bears the twelve primary 

 tentacles, becomes the ortil end in the free-living generation. 

 After the breaking up of the stolo, the peduncle and a part of 

 the stolo itself are converted into a movable proboscis, with the 

 buccal orifice, which afterwards breaks through, at its ex- 

 tremity. 



On examining serial sections of an individual already 

 separated and furnished with external tentacles, we observe 

 considerable alterations in all the three layers of the body- 

 wall. No longer containing any yolk-particles, the cells of 

 the ectoderm are quite transparent, and divide rapidly parallel 

 to their radial walls ; at the same time they rise at the surface 

 of the body into folds, so that this, in consequence, appears 

 wrinkled. However, neither at this time nor at a later 

 period does this lamina appear composed of more than one 

 layer, but always only folded. Here and there cells of the sub- 

 jacent mesoderm protrude from it and push their way into the 

 ectoderm ; these cells contain urticant elements. This cha- 

 racter is presented very distinctly in the tentacles, and 

 especially in the extremities of the feelers. The mesodermal 

 cells not only serve for the construction of the longitudinal 

 muscular fibres, but, as it appears to me, they also furnish the 

 cnidoblasts, which penetrate into the epithelial covering of 

 the body. The muscular layer consists of spindle-shaped 

 cells with very sharply contoured nuclei, and is closely applied 

 upon the ectoderm. The adhesion of these mesodermal cells 

 to the ectoderm is, as I have already remarked, not percep- 

 tible in the first stages in the primary buds ; here they are 

 rather isolated. 



8* 



