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, but 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 Entomostracous Crustacea (Water Fleas, &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 gemmce. 



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 



