84 BULLETIN OF THE 



Lastly, this formula may be applied to certain cases of fission, as in 

 fresli water Annelids. As is well known, the iissiparous process is pre- 

 ceded by the formation of the so-called budding zones (Knospungszone). 

 These arise in Ctenodrilus, according to Kennel ('82, pp. 403, 404), be- 

 tween two dissepiments in the middle of a metamere, and new ones are 

 continually formed behind the others as the animal grows in length 

 by cell proliferation at the tail end. The budding zones are, accordinu- 

 to Kennel, regions composed of embryonic cells. I think it probable 

 that this embryonic tissue has been derived from the erabrj^onic tissue 

 of the anal end of the animal. There are as many budding zones pro- 

 duced as there are new metameres added by the anal growth, and since 

 the budding zones are intrasegmental, each zooid consists of four parts ; 

 viz. (naming them from anterior to posterior end) of the posterior half 

 of the preceding budding zone, of the posterior half of the metamei-e in 

 which the budding zone arose, of the anterior part of the next follow- 

 ing metamere, and, finally, of the anterior part of the following budding 

 zone. Zooids then are made up of parts of two adjacent metameres, 

 and the middle of each zooid is intersegmental. The zooid has progressed 

 little beyond the state of possessing two (half) metameres at the time it 

 becomes free. New metameres must become formed by caudal growth. 

 The animal is, then, according to my conception of the significance of the 

 process, derived chiefly from these budding zones. Evidently, the law 

 of production of new individuals (or new budding zones) is a simple 

 OTie, and may be written, in accordance with my nomenclature, 



(19) f> E (*) * D (*) * C (*) * B (*) * A 



in which A, B, C, etc. represent successive individuals (adjacent halves 

 of two metameres), and the asterisks, as before, embryonic tissue. The 

 two adjacent asterisks together represent the budding zone, of which 

 the posterior half (parenthesized) proves itself the least active. 



The conditions given by Semper ('77, pp. 69, 77) for Chcetogaster 

 (and Nais) are much more complicated, but may be expressed by 

 the use of a formula constructed upon the same plan. Chsetogaster 

 differs from Ctenodrilus in this : that young budding zones, and event- 

 ually young individuals, are produced between older ones, instead 

 of always at the anal end ; and the new zooids often acquire sevei-al 

 metameres before becoming free. It seems to me probable that, as in 

 Ctenodrilus, the budding zones are derived ultimately from the anal 

 zone ; but here, in contradistinction to Ctenodrilus, new budding zones 

 may secondarily arise from other budding zones produced earlier, thus 



