279 
cieulus) of Schraarcla. There is also this important fact — 
that there is no segment organ in front of the first pair of 
abdominal fasciculi in Ch. diaphanus, the first segment organ 
lying between the first and second abdominal fasciculi. So 
also in the sexually mature Ch. Limncei there is no trace of 
a segment organ in front of the first pair of abdominal fasci- 
culi — that is, so far as my notes go : it is, of course, difficult 
to establish the absence of such delicate structures. Hence, 
then, I am led to infer, not only from the forward position 
that the first pair of abdominal fasciculi in the sexual Chceto- 
gaster Limncei, and in Chcetogoster diaphanus, are not the 
homologues of the first pair in the larval Ch. Limncei ; but 
the same conclusion is also supported by the disposition of 
the segment-organs. A further piece of evidence in favour 
of this view is found in the existence of structures identical 
with the “ hard pieces” of d’Udekem (PI. XIV, fig. 1), in close 
proximity to the first pair of abdominal fasciculi in the 
sexually mature Ch. Limncei. They are drawn in fig. 8, PI. XIV, 
and were observed in two different specimens. They are evi- 
dently setae or bristles modified for some generative function. 
When it is remembered that d’Udekem indicated the “hard 
pieces” in Chcetogaster Mulleri as placed at the orifices of the 
ciliated efferent ducts which he figured in that species, it 
becomes clear that if any segment organ exists in this posi- 
tion in the adult Ch. Limncei, it should be one modified so as 
to form an excretory generative duct. I am certain that such 
a duct did not exist in the specimens I studied, nor I believe 
any representative of a segment-organ. It appears to me to 
be possible that at a later stage of development than I had 
the luck to see efferent ducts may develop in connection with 
the modified set® observed by the side of the first pair of ab- 
dominal fasciculi in the sexual Ch. Limncei d In this case it 
would seem not unlikely that the first pairof fasciculi, the modi- 
fied set® and efferent ducts, may one and all be new develop- 
ments of the generative region, which in the larv® are as com- 
pletely unrepresented as are the generative glands themselves. 
This question, as well as the later stages of reproduction, 
I must hope to clear up next October. 
clearly due to a suppression of intermediate fasciculi. The apparent 
cepkalisation is thus caused; the cephalic bristles are not more truly 
cephalic than the first pair in Nais, but their separation from the next pair 
gives them a false significance. Their differentiation as to number and length 
is, however, a true claim to distinction, and is an important zoological 
character. 
1 The scattered condition of the star-like masses of spermatozoa in the 
body-cavity (see fig. 7, PI. I) is very much against the probability of an 
efferent duct developing itself. 
