34 BULLETIN OF THE 
Lastly, this formula may be applied to certain cases of fission, as in 
fresh water Annelids, As is well known, the fissiparous 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, according 
to Kennel, regions composed of embryonic cells. I think it probable 
that this embryonic tissue has been derived from the embryonic 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 zoöid 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 metamere 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, Zoöids then are made up of parts of two adjacent metameres, 
and the middle of each zoöid is intersegmental. The zodid 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 
one, and may be written, in accordance with my nomenclature, 
(19) ae E (+) * D (x) * C (*) æ B (*)* A 
in which A, B, C, ete. 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 Chætogaster 
(and Nais) are much more complicated, but may be expressed by 
the use of a formula constructed upon the same plan. Choetognster 
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 zoöids often acquire several 
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 Ctenodrilns, new budding zones 
may secondarily arise from other budding zones produced eartier, thus 
