420 WILSON. [Vot. III. 
“head-kidney”’ (Kopfniere) of Polygordius, Echiurus, and many 
Polycheta. These organs are in the form of a pair of straight 
ciliated canals situated in the anterior part of the body, above 
or at the sides of the alimentary canal, and extending into the 
head-cavity. The canals are closed internally, but open to the 
outside, according to Vejdovsky, at their anterior ends near the 
sides of the stomodzeum ; but according to the later studies of 
Bergh on Criodrilus (No. 8) the external opening is at the 
posterior end of the organ near the median line on the dorsal 
side of the body. 
The provisional nephridia ultimately degenerate and are fin- 
ally succeeded by the permanent nephridia of the trunk-region. 
Each of these arises (in Rhynchelmts) according to Vejdovsky, 
from a single mesoblastic cell situated on the posterior face of a 
dissepiment which multiplies to form a straight solid cell-cord, 
ending in front in a large cell from which the funnel is ulti- 
mately derived, and which soon acquires a closed lumen contain- 
ing a single actively vibratile flagellum. (The flagellum does not 
appear in the Lumbricidz.) This stage, which is designated as 
the pronephridium, is regarded by Vejdovsky as homodynamous 
with the head-kidney. The cilium-cell (“‘pronephrostome’’) of 
the pronephridium gives rise to the funnel of the adult, the 
glandular portion grows out as a loop-shaped lateral appendage 
from the body of the pronephridium, and the end-vesicle or 
muscular part is formed as an invagination from the ectoblast, 
which is connected with the glandular part by the persistent 
body of the pronephridium (No. 46, p. 683; No. 47, pp. 699, 
700 for figures). 
Bergh (No. 8) gives an account of the development of the 
nephridia in Crzodrilus, which agrees, broadly speaking, with 
that of Vejdovsky, but differs in the important particular that 
the entire nephridium, zxcluding the end-vesicle, is described as 
arising from the somatic mesoblast. i 
Let us now turn to the results of Meyer in respect to the 
Polychzeta (Nos. 35, 36), considering first his earlier studies, 
which were based for the most part on the study of Polymnia 
nebulosa. Meyer did not directly observe the origin of the 
end-vesicle (Endcanal), but gives reasons for his belief that it is 
invaginated from the ectoblast (Zc. p. 664). The most im- 
portant result of his work is, however, that the funnel arises quite 
