Hydra. 
Z. HYDROIDA. 
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, ;f — and seems to be the usual way of propaga- 
tion among the Hydrse 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 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 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 
* Baker, lib. s. cit. 50. f Baker ut cit. 110 — 11 : 121 — 3. 
| La generation n’est pas pour cela spontanee ; une 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 equivoque est celle ou destis- 
sus organises prealablement par un etre deja pourvu de vie, s’individualisent , 
c’est-a-dire se separent de la masse commune et participent encore, apres cette 
separation, de l’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. p. 90. Part . 
Zool. 
