72 Nils Hj. Odhner. 
they are vacuolated and distinctly show a kind of intracellular lu- 
men appearing in their efferent processes as seriate vacuoles; a 
feature which causes some resemblance with the terminal cell of a 
protonephridium, though the latter of course offers an essential diffe- 
rence in its flagellum. In the Turbellarians the protonephridia debouch 
in many cases through numerous scattered pores on the body surface, 
which may be compared with the openings of the glands in So- 
Jenogastres and it also deserves to be noted that in the latter the 
pedal gland has an intimate relation to the ventral blood vessel; 
a similar connection is also observed in the Nemertines (cf. 
WILHELM 1913, p. 137). 
This theory finds support in the fact that in the Nemertines 
»the excretory system, at one time identified as coelom, is now known 
to be epiblastic in origin (as in other worms)« (BENHAM 1901, p. 
191, after BURGER), as well as in the hypothesis set forth by LANG 
(1888), namely that the protonephridia of the Plathelminths have 
originated from dermal glandular cells which have withdrawn deeply 
into the body, and, further, it agrees well with the investigations made 
by MEISENHEIMER (1909), who derives the protonephridia (in Poly- 
chaetes, Phoronis, Lamellibranchs and terrestrial Pulmonata) from 
ectodermal invaginations; these differentiate secondarily into the 
elements characteristic of these kinds of excretory organs. 
In Chaetoderma, however, no pedal glands exist. Their sup- 
posed function as excretory organs has been taken over by the 
coelomoducts, a supposition which is quite tenable if we argue 
as follows: 
As to Chaetoderma, it may be questioned whether the »vier 
strangförmige Körper, welche v. GRAFF mit den Seitenlinien einiger 
Ascariden verglichen« (WIREN 1892 a, p. 13) represent a sort of modi- 
fied or vestigial vascular system that might be homologised with the 
pedal gland of the Neomeniina. It must be borne in mind that in 
the Nematods the side vessels may be replaced by a ventral gland, 
which seems to constitute their homologon (cf. RAUTHER 1909, p. 
531) and which is probably comparable with the pedal gland of 
the Solenogastres. Thus, through the medium of the Nematods, a 
homologisation of the original excretory organs of the Chaetoderma 
and those of the Neomeniina may be conceivable. The nature of the 
said strings is however not yet settled. In any case they seem to 
be vestigial and incapable of fulfilling any excretory function, which 
has been assumed by the coelomoducts, a modification which has 
