286 



CHAPTERS ON EVOLUTION. 



posterior part of its body. As this constriction deepens, a new head, 

 eyes, and tentacles are seen to be formed at the spot in question 

 (Fig. 192), and a second nai's is thus viewed 

 budding from the hinder extremity of the ori- 

 ginal individual. This new being, produced 

 thus by the division of the parent body, 

 sooner or later becomes detached therefrom, 

 and seeks an independent existence. Cases 

 have been observed in which as many as six 

 new individuals have been produced from a 

 single nai's. In Cirrhatula, another worm- 

 genus, Miiller relates that he found three new 

 individuals adherent " in one length." " The 

 mother," he remarks, 

 "had thirty pedate 

 segments; the young- 

 est daughter, or that 

 nearest the mother, 

 had eleven, but the 

 head was not yet de- 

 veloped. The most 

 remote had seventeen 

 rings, with both head 

 and eyes, and, more- 

 over, the tail of the 

 mother ; the middle 

 one had seventeen 

 segments and a head." 

 It is matter for re- 

 mark that no egg- 

 producing organs exist in the new individuals 

 thus budded, which may therefore be named 

 "neuters," like the "workers" among the 

 bees. The last-formed individual, however, 

 in the na'is, develops reproductive organs, 

 and thus the continuance of the species in 

 time is duly provided for. 



In connection with the production of like FIG. 193. JOINTS OF LOBSTER. 

 parts by budding a process known as that 



of " vegetative repetition " of parts, and producing what is known 

 as the " serial homology " of animals it is interesting to note that 

 the twenty joints or so of which an anima !like the lobster (Fig. 

 193) is composed, are constructed, irrespective of size or function, 

 upon one and the same type. The same remark holds good of an 

 insect, of a centipede, of a spider, or other articulated animal. Very 



FIG. 192. NAIS, OR FRESH- 

 WATER WORM. 



