554 GEMMIPAROUS REPRODUCTION OF LOWEST ANIMALS. 
which have been already described (§122) in the Hydra. But 
not unfrequently in this species, and ordinarily in many others, 
the body divides into two equal parts, in each of which we see 
a mouth and other parts resembling those of the original. This 
division is gradual. A narrowing of the body along or across 
its middle (for the fission or cleavage sometimes takes place 
lengthways, as at 5, sometimes transversely, as at c), is first 
seen; the indentation at the edge becomes gradually deeper, 
and at last the two parts hold together by but a narrow band, 
which finally breaks, and they become free.—The same 
method of multiplication is observed among the simple 
Rhizopoda (§ 129); but when the gemmae remain connected 
with each other, as in Zoophytes, we have such composite 
fabrics as are presented to us in the classes of Foraminifera 
(§ 131) and Sponges (§ 136). 
726. Reproduction by Gemmation is most characteristically 
seen among the Radiated classes; and in none better than in 
the Hydra already so frequently referred-to. Although this 
interesting little animal sometimes reproduces itself by true 
sexual generation (§ 734), yet its usual mode of propagation 
is by buds (§ 122), as shown on the left hand side of the ac¬ 
companying figure (fig. 296). And, as already explained, it 
is by this same process of gemma¬ 
tion that the arborescent struc¬ 
tures of the Composite Zoophytes 
are formed; the gemmae not de¬ 
taching themselves, but remaining 
as parts of the common stock (§§ 
124,127). In some of those, how¬ 
ever, which are formed upon the 
plan of the Sea Anemone (§ 126), 
the multiplication (fig. 297) is ef¬ 
fected rather b y fission or division 
into two equal parts (as among In¬ 
fusoria), than by the out-growth of 
buds. We have already had occa¬ 
sion to notice (§ 125) the very re¬ 
markable form of gemmation that 
takes place among Zoophytes, giv¬ 
ing origin to independent beings 
which seem to belong to a class altogether different, but which 
Fig. 296. —Hydrj: (attached to duck¬ 
weed) : one of them developing buds. 
