Or 
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POST-LARVAL STAGE OF ARENICOLA MARINA. 
As to the separate existence of a somatic ceelomic epithelium I 
feel some doubt ; apparently the inner ends of the cells giving rise to 
the longitudinal muscles are themselves the lining of the ccelom, so 
that these cells are myocwlomic. 
The nephridia are confined to Somites 6—10, though there may 
be traces of them in other somites. I believe I can distinguish a 
small one, for instance, in Somite 5. They have thus the same 
position as in the adult, where they occur in the fourth to eighth 
cheetigerous somites, 7. e. Somites 6—10. 
But though they have the same position, they are very different 
in shape. I have previously figured this organ in the adult (Quart. 
Journ, Mic. Sci., xxxu, pl. xxv, The Nephridium of Lumbricus, §c.), 
and the present fig. 6 may be compared therewith. In place of the 
great wide sac there is in the post-larval stage quite a simple narrow 
tube, running nearly in a straight line from the nephridial pore, 
situated behind the ventral bundle of chete, forwards to the 
nephrostome, about midway between that bundle and the preceding 
one. The tube is, however, divisible into two regions, according to 
the presence or absence of concretions. The former (fig. 6, a) forms 
rather more than half the whole length of the tube. The organ is 
ciliated throughout. 
The nephrostome is perfectly simple, so far as I can judge; is 
without lips, so that we cannot speak of a ‘ funnel ” in the usual sense 
of the word. 
With regard to the alimentary tract, it presents exactly the same 
regions as in the adult. The narrow cesophagus passes back from 
the pharynx (? if this is eversible) into a wide “ stomach,” occupying 
Somite 7 and part of 8. Into the hinder part of this a pair of 
cone-like diverticula open, each diverticulum being longitudinally 
ridged internally. Immediately after the stomach the gut presents 
a series of pouches on each side, as in the adult. This sacculated 
region extends through four or five somites, and is succeeded by 
the narrow intestine, which suddenly dilates in the “ tail,’ and here 
occupies nearly the whole cavity of the body. 
