GEMMATION. 35 



fluid of the perigastric space. It sometimes remains stationary, with the uncihated portion, 

 in which the polypides are suspended, protruded from the cihated (PI. XI, fig. 32) ; but 

 most frequently this uncihated portion is withdrawn within the ciliated, which is then closed 

 over the aperture (PI. XI, fig. 33). In this condition the little animal assumes a piriform 

 figure, with the small end corresponding to the aperture. It is thus carried through the 

 surrounding fluid by the vibration of its ciha, performing rapid and elegant motions, always 

 swimming with the broad end foremost, and at the same time revolving gracefully on its axis. 



The complete evagination of the uncihated portion is still prevented by the bands already 

 mentioned, but we now find that these bands, which must not be confounded with the 

 permanent parieto-vaginal bands of the adult, have disappeared, and the evagination has 

 become complete (PI. XI, fig. 34). The uncihated portion is now no longer capable of being 

 withdrawn within the ciliated, with which it has become directly continuous, while the ciha 

 themselves disappear from the ciliated portion, and the entire sac becomes enveloped in an 

 ectocyst, to constitute the cell of the adult polyzoon. The subsequent changes are produced 

 by the gemmation of new polypides, with their proper ectocysts and endocysts. 



Phcmatella fruticosa presents similar developmental phenomena ; the ciliated larva, 

 however, in this species, differs from that just described, in having its polypide single (PI. XI, 

 fig. 35). 



If a specimen of Alcyonella funrjosa be cut into small pieces, under water, in the month 

 of July or August, the ciliated embryos will be liberated in abundance, and may be examined 

 with facility. 



Gemmation. — The development of gemmae has already been partially traced in the 

 description just given of the larva of Alcyonella ; we must now follow it, however, a little more 

 in detail, as it is presented by the buds formed in the adult polyzoon. 



With the exception of some peculiar forms of gemm£B, to be presently described, these 

 bodies always originate in the endocyst. In Lop/iojms, Alcyonella, Pliimatella, and Fredericella, 

 they occur without any very regular order near the orifice of the cell. In Oristatella the gemmae 

 are produced very regularly from constant points on the sides of the previously existing cells, 

 and the new cells thus produced remaining in apposition with one another, and never becom- 

 ing extended into branches, constitute several concentric series on the surface of an expanded 

 disc. In Paludicella they also arise with much regularity from fixed points a little below 

 and at each side of the orifice of the previously formed cells ; and here, not continuing in 

 apposition, the new cells form branches, which, from the fixed points at which they originate, 

 and the constant angle at which they are given off from the parent-cell, confer upon the 

 whole colony a greater regularity than is met with in the other branched forms of the fresh- 

 water Polyzoa. 



Most of the steps in the development of the gemma may be traced with considerable 

 facility in Paludicella. In the earliest condition in which I have been able to observe it, the 

 gemma appears here as a minute tubercle, projecting from the external walls of the cell, and 

 filled with a granular parenchyma (PI. XT, fig. 1). It now becomes elongated (fig. 2), and we 

 soon find it aoiiowed out into a cavity, which communicates with the interior of tiie parent- 

 cell. The tubercle, with its cavity, increase in size, and the gemma (fig. 3) is now found to 

 consist of an external envelope, continuous with the ectocyst of the parent-cell, and of a thick. 



