Fig. 9. 



Fig. 11. 



HYDROIDEA. 



But to understand better this process, we may refer to one or two 

 enlarged figures of species. Figures 3, 3a, 9, 10, and II, represent the 

 principal varieties among the Sertularidse. In figure 9, there is a 

 single range of calicles on the stem, the polyps of which are con- 

 nected with the tubular cavity within. The 

 polyp c is a bud 'from B, and B from A. 

 We perceive from the figure that the first 

 step here in the budding process, is a length- 

 ening upward of the tubular axis, from the 

 polyp below: after elongating to a certain 

 distance, the bud commences to form, and 

 finally, from the side of the ascending shoot, 

 the new polyp B starts out. The main 

 trunk continues elongating, and, after a 

 similar interval, another bud forms in like 

 manner. The same process is illustrated in 

 figures 3 and 10; the only difference con- 

 sists in the formation of two buds on oppo- 

 site sides of the axis, almost simultaneously. 

 Figure 3 represents the apex of a branch, 



with the two buds, developed at the extremity of the tubular axis, 

 and, in figure 10, the tubular axis is elongated between the buds, 

 preparatory to a continuation of the budding process. Although 

 nearly opposite, the polyps often become alternate afterward, as is seen 

 in figure 3a, which represents a lower part of a branchlet. More- 

 over, the apparent jointing above, often becomes afterwards quite 

 indistinct. In figure 11, we have an example of a periodicity in the 

 budding process. 



The formation of the young Hydra seems at first to be a very diffe- 

 rent process from the budding of a Sertularia, yet is closely analo- 

 gous : the only essential peculiarity consists in the young polyp's 

 detaching itself and becoming free instead of being persistent. The 

 apparent discrepancies are owing to the absence of calicles or a coral- 

 lum, and the erect mode of growth in the parent, instead of oblique; in 

 the Hydra the buds form as lateral shoots from any part of the lateral 

 surface; while in the species above explained, with oblique polyps, the 

 upper part of one side of the visceral cavity gradually lengthens and 

 buds. Some little variety in the budding process is exhibited in other 

 groups among the Hydroidea ; but the above will suffice to explain 



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