274 
the ventral nerve-cord, in the region of the stomach, rounded 
masses of ova develop in pairs . 1 
Appearance of the Sexual Forms. — The asexual zooids of 
Chcetogaster limnaei, which are so abundant on the water- 
snails through the greater part of the year, are rarely more 
than one sixth of an inch long, and then usually consist of 
two well-grown individuals, with portions of some four others 
developing between and behind them ; for details of their 
structure I must refer to my paper in the ‘ Linnsean Trans- 
actions.’ In October I observed some of the worms, which 
appeared to be unusually large, and I accordingly examined 
them with the microscope. They left the body of the snail 
when placed in a vessel of water, in a bolder and more ven- 
turesome manner than I had ever noticed with the usual 
small forms, which stick very close to their snail, especially 
when they are sought in order to he submitted to an examina- 
tion. One of these large worms gave the following order of 
bristle-bundles (which I shall henceforth call fasciculi), in- 
dicating segments, individuals, and new regions of growth, 
viz., head with cephalic bristles, followed by five well-grown 
abdominal fasciculi (instead of three with a growing fourth, 
as is the case in the asexual zooids generally), then a space, 
and homogeneous matter indicating a region of growth ; then 
three very incomplete fasciculi ; then another space and con- 
striction ; then ten abdominal fasciculi, the anterior of which 
were well grown, the posterior just sprouting ; behind this, ho- 
mogeneous matter and a constriction; and then a head with 
cephalic fasciculi, followed by five abdominal pairs ; after these 
a constriction and seven abdominal fasciculi, the anterior well 
grown, the posterior rudimentary. The succession may be 
written thus : 
ceph. and 5 abd. | 3 abd. | 10 abdominal | cepli. and 5 abd. | 7 abdominal, 
and compared with a parallel case of an asexual zooid — 
cepb. and 3 abd. | 3 abd. | 6 abdominal | ceph. and 3 abd. | 9 abdominal. 
The important thing to observe is the succession of five 
well-developed pairs of abdominal fasciculi in immediate 
connection with the head in the case of these larger speci- 
mens, which I soon found were developing sexual organs ; for 
1 M. Claparede, in his most valuable ‘ Recherches sur les Oligochetes,’ 
accepts d’Udekem’s statements as to the presence and position of an efferent 
duct in Chaetogaster. In any case, it cannot be allowed that the hypothetical 
duct is developed in the second segment, as M. Claparede tabulates it, for 
the pharyngeal region of Chcetogaster probably represents the second and 
third somites (perhaps more) of other Oligochmta. 
