554 GEMM1PAROUS REPRODUCTION OP 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 6, sometimes transversely, as at c), is first 

 seen j 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 j 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 by 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. HYDIUE (attached to duck- 

 weed): one of them developing buds. 



