Fissiparous Species of Tubicolar Annelid. 127 



more lately by Quatrefages as occurring in Syllis prolifera is 

 very nearly simple fission, the animal dividing near its 

 middle, and the under half, before separation, only putting 

 forth, as buds, those appendages which are characteristic of the 

 head. 



Secondly, Milne-Edwards has described in Myriadina a 

 prolification by a sort of continuous budding between the anal 

 and the penultimate segment. A new ring is produced be- 

 hind the penultimate segment, and this enlarging gives rise to 

 a new ring posteriorly, and so on until the bud attains its full 

 length. 



It would seem possible that the second mode of prolifica- 

 tion in Nats, described by 0. F. Mtiller, is in reality the same 

 as this, though he describes the new growth as entirely result- 

 ing from the excessive development of the anal segment. 



Thirdly, M. Schulze, an excellent observer, has described 

 a third very singular mode of prolification in Nats, whence the 

 long chains of zooids occasionally observed arise. For when, 

 by the fissive process the Nais is divided into an anterior and 

 posterior zooid, the last segment of the former greatly enlarges, 

 becomes divided into segments, and the anterior of these be- 

 coming a head, a new zooid is formed between the previously 

 existing ones ; this process is repeated in what was the pen- 

 ultimate, but is now the ultimate segment of the anterior zooid ; 

 and, again, in the anti-penultimate, so that at least a long 

 string of zooids is formed, each of which, except the last, is 

 produced from a single segment. 



Fourthly, According to Frey and Leuckart, whose observa- 

 tions have been confirmed by Krohn (Wieg. Archiv., 1852), 

 Autolytus prolifer multiplies in a somewhat similar way, but 

 instead of each new interposed zooid being formed at the 

 expense of a fresh segment of the anterior zooid — it is pro- 

 duced by the metamorphosis of a bud, or rather of a mass of 

 blastema the equivalent of a bud, developed from the under 

 extremity of the last segment of the anterior zooid. 



Supposing further observation to confirm the distinctness of 

 all these modes of prolification, they might be classified accord- 

 ing to the amount of the already formed parental organism 

 which enters into the produced zooid. 



