1912. |] J. SterHeNsoN : Indian Aquatic Oligochaeta. 231 
From this it follows, that variations or irregularities in the 
process of budding will give rise to corresponding variations or 
irregularities in the degree and form of cephalization. 
That the budding zone varies in position has been known for 
some time. It is usual, following Bourne (5), to denote by 
the number of segments of the original animal behind which the bud- 
ding zone appears, and though Bourne thought at first that 1 would 
be found to be constant for each species, it now appears that in 
a large number of species at least it varies within somewhat wide 
limits (for examples, cf. Benham (3), Piguet (11), Stephenson (16) 
(Stylaria lacustris) ).1 
Variations in position of the budding zone would not neces- 
sarily affect the number of cephalized segments ; the point has been 
mentioned, because variations in one respect prepareus to look for 
variations in other respects. Such have been noted in Nas 
commums by Piguet (11) :—‘‘ a diverses reprises, j’ai trouvé un 
certain nombre d’exemplaires qui n’avaient que 4 segments 
avant celui ott débutent les soies dorsales et les cellules chlorago- 
génes(normalement, le 6me). J’ai d’abord pensé 4 une régénération 
incompléte aprés mutilation; mais tous ces individus avaient la 
région antérieure absolument normale, sauf que leur 5me segment 
étail homologue du 6me des autres. Il faut done supposer que 
le bourgeonnement produit quelquefois, accidentellement peut- 
étre, des spécimens ayant, dans la region du pharynx et de 
’oesophage, un segment de moins que les autres.’? The fact that 
in Branchiodrilus hortensis there may be either four or five cepha- 
lized segments (15) belongs here also. And in Slavina punjabensis 
I found (14) a number of irregularities in the results of the budding 
process ;—incomplete differentiation of the head, an eye wanting 
on one side, fewer setal bundles, and these containing fewer setae 
than normal ;—which might perhaps be partly explained by suppos- 
ing that separation of the two individuals had taken place before 
the differentiation of the head had been completed, and that this 
differentiation would follow after, instead of as usual coming 
before, the separation. But it isperhaps equally likely that these 
irregularities were destined to endure. 
This brings us to the condition in B. menont. We have here 
before us a number of variations in the characters of the anterior 
end of the animal, especially in the numbers of the ventral setal 
bundles in front of the gills (or of the first dorsal setae). As to 
how this is related to the process of asexual reproduction, and 
how far these variations may be due merely to a delayed differen- 
tiation of the newly formed head, see the section on Asexual 
Reproduction. Referring to the discussion there for support, 
it will be sufficient now to state that im B. menoni we have a 
species which varies within wide linnts in regard to cephalization, as 
manifested especially in the setal distribution. 
| In the Aeolosomatidae however and in the genus Chaetogastey, in which cases 
the number of body segments is small, 7 would seem to be fixed for each species, 
according to observations on all the species that have come under my notice. 
