HYDRA. 81 



Enlargement of the whole against January showed the advantage of 

 their new position, where the height of the shell sustaining them had been 

 so adjusted that food at the bottom of the jar was attainable by their ex- 

 tended tentacula. 



The group had augmented to 25 on the Ist of April, when a fragment 

 of the shell, with seven individuals, accidentally separated, leaving the 

 other 18 adhering to the suspended portion. This latter alone continued 

 under observation, the fragment being abandoned. 



Supervening changes and a series of other accidents befell the group 

 from the fragility of the shell. Portions of the surface, yielding in decay, 

 carried off the animals adhering to them. But in August of the following 

 year, or about 21 months from the commencement of observation, the 

 group was crowded and beautiful. — Plate XIII. fig. 2. 



The greater proportion of the whole separated seven months later, in 

 April, and at length only six remained adhering in two years and a half 

 from the beginning. One of them, if not belonging to the original ten, 

 was of the first generation. The last of these six was detached in the 

 following June, or in 32 months from the November first specified, when 

 the shell proved so brittle that it crumbled to the touch. 



Though many individuals which had formed the bulk of the group 

 were preserved, their history, as a community, was prosecuted no longer. 

 It is not that condition which admits the satisfactory elucidation of 

 details. 



The anatomical structure of the hydra proper has been as yet but in- 

 sufficiently explained. In as far as I am informed, no muscular formation 

 is ascribed to its parts, though certainly endowed with muscular powers : 

 nor has any nervous or circulatory system been detected, though life and 

 sensation be evident in the remotest extremities. Some have lately af- 

 firmed the existence of ova or their rudiments, thus reviving an earlier 

 opinion, indeed the earliest of all, omne animal ex ovo. But I understand it 

 to be a desideratum on the whole, among the most skilful naturalists, that 

 many assertions were confirmed by undoubted experiment and observation 

 anew. 



Confining myself, however, to the origin of this marine hydra, and 

 VOL. I. L 



