224 HIGHWATEK MARK. 



Besides these spines, another organ of defence is 

 conspicuous, in the form of a branched projection 

 guarding the membrane-covered aperture. From the 

 inner margin of this aperture (or that which is next 

 to the median line of the two-rowed branch) springs 

 a shelly flat plate, which spreads laterally and divides 

 into two, these into two more, and these in most in- 

 stances with an incipient bifurcation again. Hence 

 results a wide fan-shaped organ, which, arching over 

 the membrane, protects it from violence, while it 

 does not interfere with the projection of the animal 

 out of the valvular opening, nor impede the ciliary 

 currents which bring food and oxygen for its re- 

 quirements. 



Here and there, on looking carefully over several 

 branches of the little shrub, we see one and another 

 cell crowned by a globular body resembling a little 

 pearl. This is an egg-cell ; wherein are developed 

 these gemmules, which when matured escape from 

 their prison and swim away to form a new generation. 

 These ova are not produced till the composite struc- 

 ture has attained considerable maturity; and the 

 result of their liberation must not be confounded with 

 that of the progressive budding forth of the compound 

 tree. The one is analogous to the multiplication of a 

 plant by cuttings, or rather by the successive growth 

 of its twigs ; the other to the formation of a new race 

 of plants by the agency of ripened seeds. 



Another interesting point, which would arrest your 

 notice, is the number of long tubular filaments, which 



