338 Natural History of Britisli Zoophytes. 



tion among the Hydrae during- the summer months. But in autumn 

 the Hydra generates internal oviform gemmules which, extruded from 

 the body, lie during the winter in a quiescent state, and are stimulat- 

 ed to evolution not until the return of spring and its genial weather. 

 Few observations have been made on these apparent ova, so that their 

 structure, their source, their manner of escape from the body, and 

 their condition during winter are scarcely known, Trembley de- 

 scribes them as little spherical excrescences, of a white or yellow co- 

 lour, attached to the body by a very short pedicle. He never saw 

 more than three on the same polype. After sometime they became 

 separate, and fell to the bottom of the glass of water in which the 

 creatures were kept, where they came to nothing, excepting one only 

 which was presumed to have evolved into a polype, for although 

 his experiment renders this conclusion probable, it was still rather an 

 inference than an actual observation, so much so, that Trembley con- 

 tinued to entertain doubts of their nature. Jussieu, it seems, con- 

 ceived that each little excrescence was a vesicle filled with ova of 

 microscopic minuteness, but there is no foundation for any such hy- 

 pothesis.* 



These are the modes in which the Hydra naturally multiplies its 

 kind, but it can be increased, as already hinted, by artificial sections 

 of the body, in the same manner that a perennial plaut can be by 

 slips and shoots. If the body is halved in any direction, each half 

 in a short time grows up a perfect Hydra ; if it is cut into four or 

 eight, or even minced into forty pieces,f each continues alive and de- 

 velopes a new animal, which is itself capable of being multiplied in 

 the same extraordinary manner. If the section is made lengthways, 

 so as to divide the body into two or more slips connected merely by 

 the tail, they are speedily resoldered, like some heroes of fairy tale, 

 into one perfect whole ; or if the pieces are kept asunder, each will 

 become a polype, and tbuis we may have two or several polypes with 

 only one tail between them ; but if the sections be made in the contrary 

 direction — from the tail towards the tentacula — you produce a mon- 

 ster with two or more bodies and one head. If the tentacula, — the 

 organs by which they take their prey, and on which their existence 

 might seem to depend, — are cut away, they are reproduced, and the 



* Trembley, Mem. 196 — 7. 



f " J'ai ouvert siir ma main un Polype, je l'ai etendu, et j'ai coupe en tout 

 sens la peau simple qu'il formoit, je l'ai reduit en petits morceaux, je l'ai en 

 quelque maniere hache. Ces petits morceaux de peau, tant ceux qui avoient 

 desbras, que ceux qui n'en avoient point, sont devenus des Polypes parfaits." — 

 Trembley, Mem. 248. 



