Studies on Earthworms. - Journal of Cell Science

256 WILLIAM BLAXLAND BENHAM.
These corpuscles can readily be seen by killing a piece of
tissue, such as a septum or a nephridium, with -j^- per cent,
osmic, and then staining in picrocarmine.
The Eephridia.—These have been figured by Gegenbauer
(10) and described histologically by Claparede (11) for Lnmbricus.
Each nephridium or "segmental organ" of Dr.
Williams (47) is a more or less coiled tubule with an internal
funnel-shaped opening at one end, and an external pore at
the other. The tube itself is divisible into three regions,
the innermost leading from the funnel is cilated internallythis
leads to a glandular region, and this to a short, muscular,
slightly enlarged " vesicular " region. The lumen of the first
two regions is intracellular, whilst that of the vesicle is intercellular
and surrounded by muscle-fibres. The histology of
the nephridia has not been minutely studied in any form,
except in Lumbricus.
Nephridia are at present known in nearly all the forms
whose internal anatomy has been described.
In Digaster Perrier appears not to have detected the organ
or its pore. Beddard did not find them in Pleurochseta.
In most of the Perichsetas they are so small as to have
led to the impression that they are absent, but in P. robusta
and P. affinis delicate tubules are attached to the septa, but
Perrier gives no details. [In a Perichseta from the Philippines
I have found numerous small nephridia in each
somite by means of sections. Beddard informs me that he
has made a similar observation.]
In the worms which possess nephridia the internal funnel
is usually situated in the somite anterior to that in which the
tubule lies, but in Plutellus the whole organ lies in one
somite, and it has a large vesicular portion.
In Typhaeus the nephridia have only been observed in the
anterior somites.
In Titanus the nephridia do not commence till somite xiv.
In Anteus those of the clitellar region are shorter, wider,
and less coiled than the others, and are supposed by Perrier
to function as sperm ducts.