THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 105 



that among higher types we have long strings of similarly- 

 formed gemmae which do not become individually independ- 

 ent, but separate into organized groups; and that from 

 these we advance to forms in which all the gemmae remain 

 parts of a .single individual. One other significant 



fact must be added. There are cases in which annelids 

 multiply by lateral gemmation.* That the longitudinally- 

 produced gemmae which compose an annelid, should thus 

 have, one of them or several of them, the power of laterally 

 budding-off gemmae, from which other annelids arise, gives 

 further support to the hypothesis that, primordially, the seg- 

 ments were independent individuals. And it suggests this 

 belief the more strongly because, in certain types of Ccelen- 

 terata, we see that longitudinal and lateral gemmation do 

 occur together, where the longitudinally-united gemmae are 

 demonstrably independent individuals. 



§ 207. Though it seems next to impossible that we shall 

 ever be able to find a type such as that which is here sup- 

 posed to be the unit of composition of the annulose type, 

 since we must assume such a type to have been long since 

 extinct, yet the foregoing evidence goes far towards showing 

 that an annulose animal is an aggregate of the third order. 

 This repetition of segments, sometimes numbering several 

 hundreds, like one another in all their organs even down to 

 those of reproduction, while it is otherwise unaccountable, is 

 fully accounted for if these segments are homologous with 

 the separate individuals of some lower type. The gemma- 

 tion by which these segments are produced, is as similar as 

 the conditions allow, to the gemmation by which compound 



* In place of those originally here instanced about which there are dis- 

 putes, I may give an undoubted one described by Mcintosh, the Si/Uis 

 ramosa, a species of chaetopod living in hexactinellid sponges from the Ara- 

 fura Sea, which branches laterally repeatedly so as to extend in all directions 

 through the canals of the sponge. In most cases the buds terminate in oval 

 segments with two long cirri each. But male and female buds were found, 

 provided each with a head, and containing ovaries and testes. Sometimes 

 these sexual buds had become separate from the branched stock. 



