260 



ANALYTICAL INDEX. 



CHAPTER III.— The Hydra, ok Polypus, .... page 73 



Hydra a conventional name, . . . . . ib. 



This work is a collection of memoirs, ... ib. 



Dr Johnston's partition of Zoophytes, . . . . ib. 



Two species of fresh-water hydrge in Scotland, one in the sea, 74 



Nature of all three corresponds, . . . . ib. 



Hydra gelatinosa, tuba, and strobila, are the same animal, . 76 



§ 1 . Hydra tuba, the Trumpet Polypus, 

 Miiller, Sars, Lesson, 

 British Association at Edinburgh, 1834, 

 Hydra, analogies of, with the Actinia, 

 Food, ..... 

 Senses obtuse, 



Propagation, .... 

 Generates in its own likeness. 

 Reproduction in the vicinity of the stomach. 

 Embryo buds from the parent, 

 Sertularia encreases like the hydra. 

 Colony of 83 Hydrffi from one parent, 

 Eight the original complement of tentacula, 

 "Works of Nature resolve into simplicity. 

 Lost parts regenerated. 

 Each of two halves becomes perfect. 

 Symmetry always restored. 

 Conclusions from experiment. 

 Propagation depends on sustenance. 

 Imperfect animals do not propagate. 

 Colonies observed during years. 

 Plates XIII., XIV. explained, 



76 

 ib. 

 ib. 

 77 

 ib. 

 78 

 82 

 ib. 

 ib. 

 ib. 

 86 

 87 

 88 

 89 

 90 

 91 

 ib. 

 93 

 95 

 ib. 

 96 

 97 



§ 2. Origin op the Hydra tuba. 



Type of the multiplication of zoophytes, 

 Vorticella, Plates XII., XXII., 

 Hydra tuba larger than other hydrse, 

 The parent survives posterity. 

 Medusa or Sea-blubber, 

 Certain species noxious, Plate XV., 

 Its progeny resembles the planula, 

 Progeny metamorphoses to the Hydra tuba, 

 JIultitude of planulae in ovarian sacs. 

 Young hydra has eight arms or tentacula, 

 Eleven prolific Medusae, Plate XVII., 



99 



ib. 

 100 



ib. 



ib. 

 101 

 102 

 103 

 105 



ib. 



ib. 

 106 



