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first, as I believe, of the larva. At septum No. 5 the stomach 
ended ; that is to say the dilatation of the alimentary canal 
ceases, a great contraction occurs, and a second expansion 
follows, forming what may be termed intestine, for the sake 
of distinction. Between septums 5 and 6, 6 and 7, and 7 and 
8, there was a pair of segment organs and a pair of fasciculi, 
in each case. These were followed by homogeneous blastema, 
and the commencement of another zooid, to which succeeded 
a third zooid, developing sexual organs like the first. In the 
course of time, no doubt, each of these zooids would complete 
itself by developing the full number of sixteen or seventeen 
segments, perhaps even a larger number than I saw in the 
specimen, PI. XIV, fig. 2. 
The Testis . — The testis is seen in PI. XIV, figs. 5, 7. In the 
first case it is immature, in the second figure it is in a worm ap- 
parently quite adult ; fissiparity had entirely ceased ; the worm 
had the appearance given in fig. 2 ; and the generative pro- 
d uc ts, both ova and spermatozoa, werefloating freely in the body 
cavity. The large spheres of which the testis is at this time 
composed appear to be thrown off, as they become complete, 
into the perivisceral cavity, where they assume the form 
(fig. 7), the well-known actinophrys-like masses of sperma- 
tozoa. These pass down the body to some distance, making 
their way so far as the third or fourth pair of abdominal fas- 
ciculi. There certainly appeared to be no efferent duct in 
connection with the testes at this period of maturity. Whether 
a pair are developed, or how the spermatozoa escape, is 
unknown to me. 
The Clitellusand Genital Setce . — The clitellus extends from in 
front of the first pair of abdominal fasciculi to behind the second 
pair. It consists of cells having the appearance of PI. XIV, fig. 
9. The presence of a clitellus implies copulation ; but the 
only other copulatory organs are possibly the stunted bristles 
which develop near the first fasciculi. To these remarkable 
organs I propose to give the name of genital setae. 1 A clitellus 
implies copulation, if the usual explanation of its function is 
correct ; but it seems to me to be quite as well suited to the 
purpose of forming an egg-capsule as to aiding copulation — 
in fact, rather better. In the Earthworm it probably is 
useful in sexual congress ; but it by no means follows that 
because such is its function, or a part of its function in the 
Earthworm, that such is its function elsewhere. An existing 
1 I have recently observed similarly modified setae in Nais, which develope 
as a new pair of fasciculi, indicating a segment unrepresented in the asexual 
form. Thus the existence of distinct larval and mature forms is established 
for gemmiparous Oligocheeta. 
