Hydra. Z. HYDKOIDA. 105 



mark where it had been protruded." — " After a young polype once 

 gets all its arms, it alters indeed in size, but neither appears to shift 

 its skin, or undergo any of the changes most other insects do." * 



Instead of buds or little protuberances, the body sometimes push- 

 es forth single tentacula scattered irregularly over it, and these ten- 

 tacula can be metamorphosed into perfect polypes, the base swelling 

 out to become the body, which, again soon shoots out additional ten- 

 tacula to the requisite number ! f 



This is a mode of generation which the term viviparous does not 

 correctly embrace, unless we give to that word a signification so ex- 

 tensive as to include all generations which are not oviparous : It is 

 an example of equivocal, or what some foreign physiologists deno- 

 minate, the generation by the individualisation of a tissue previously 

 or already organised, jj — and seems to be the usual way of propaga- 

 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- 

 sci'ibes 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 some time 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 x'ather 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 



" Baker, lib. s. cit. 50. t Baker ut cit. 110—11 ■. 121—3. 



\ La generation n'est pas pour cela spontanee ; una generation spontanee doit 

 etre la production d'un etre organise de toutes pieces, lorsque des elemens in- 

 organiques se reuniront pour produire un animal, une plante. Cette generation 

 est impossible, et n'a jamais lieu. Une generation equiuoque est celle ou des tis- 

 sus organises prealablement par un etre deja pourvu de vie, sHndividualisent, 

 c'est-a-dire se separent de la masse commune et participent encore, apres cette 

 separation, de I'etat dynamique de la masse, c'est-a-dire de sa vie, mais, a son 

 propre profit. C'est ainsi qu'un tissu produit un Entozoaire. C'est de la vie 

 continuee." — Ch. Morren in Ann. des Sc. Nat. an. 1836, Vol. vi. j). 90. Part. 

 Zool. 



