556 GEMMATION OF ARTICULATA AND MOLLUSCA. 
preceding joint, which at last divides. Previously to its separa¬ 
tion, however, the young one often shoots out another from 
its own last joint, in a similar manner; and three successions 
have thus "been seen united. In some species of Nereis , the sepa¬ 
ration takes place nearer the middle of the body (fig. 298). In 
the greater number of cases, however, in which such a detach¬ 
ment of the posterior part of the body of Annelids takes place, 
the separated gemma does not contain the structure of the entire 
animal, hut consists of little else than the generative apparatus, 
endowed with locomotive organs; so that this process of mul¬ 
tiplication does not so much correspond with the ordinary pro¬ 
pagation by buds, as with the peculiar development and throw¬ 
ing-off of generative buds to be presently described.—Among 
the higher Articulata, we do not meet with any instances of 
ordinary gemmation; but the non-sexual production, which 
is now known to take place not only in the Aphides (§ 746) 
but in many other Insects, as well as in Rotifera (Wheel- 
Animalcules) in Entomosiracous Crustacea (Water Pleas, &c.), 
and probably in some higher Crustacea, must be regarded as 
a peculiar form of the same process ; the offspring being pro¬ 
duced from eggs, which have the power of self-development 
without sexual fertilization, and which must therefore be 
accounted internal gemmae. 
728. In the Molluscous series, the power of multiplying by 
gemmation appears to be limited to the Tunicata (§ 114) 
and the Polyzoa (§ 115); being restricted in the first of 
these classes to a section of the group ; whilst in the second, 
which closely follows the habit of Zoophytes, it seems to 
be universal. The bud arises in some instances directly 
from the body; but in other cases it is put forth by a stolon 
or creeping stem that connects all the bodies together 
(fig. 63). Among the Polyzoa the buds usually remain in 
connexion with the parent-stock, so as to form composite 
fabrics so closely resembling those of Zoophytes as to be com¬ 
monly ranked with them. And the like happens also among 
the Compound Ascidians. But where gemmation takes place 
among the solitary Tunicata, the bud becomes detached, and 
maintains a perfectly independent existence. There is a very 
curious case of internal gemmation among the Salpce (a tribe 
of Tunicata which are not attached, but float over the waves); 
for the buds are developed, not from the exterior of the 
