. Animal physiology. Physiology, Comparative. 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 originah This division is gradual. A narrowing of the body along or across its middle (for the Jission 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 la
. Animal physiology. Physiology, Comparative. 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 originah This division is gradual. A narrowing of the body along or across its middle (for the Jission 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 SiMnges(^ 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 tliis interesting little animal sometunes reproduces itself by true sexual generation (§ 734), yet its usual mode of propagation is by huds (§ 122), as shown on the left hand side of the ac- companying figure (fig. 296). And, as already explained, it is ])y this same process of gemma- tion that the arborescent struc- tures of the Composite Zoophytes are formed; the gemmas not de- taching themselves, but remaining as parts of the common stock (§§ 124,127). In some of those, how- ever, which are formed u2:»on the plan of the Sea Anemone (§ 126), the multiplication (fig. 297) is ef- fected rather hj Jission or division into two equal parts (as among In- fusoria), than l^y 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 independen
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